The reasons players switch clubs are many. They might be unwanted, wanted by a bigger fish, or it may be down to their contractual situation. Gabriele Marcotti identifies 50 who could be packing their bags either in this transfer window or in the summer. From Ronaldinho to Ronaldo, they're in no particular order.
50. Ronaldo, 31, AC Milan
Yes, he's still around. And sooner or later Milan may decide they're tired of waiting for him to get fit. Which means he'll need to be "rescued", possibly on loan. A gamble? Of course. But if you're romantic and you remember that he remains one of the greatest goalscorers of his generation (61 international goals and counting . . .) he may be hard to turn down.
49. Stephen Hunt, 27, Reading
Won't win popularity contests, but the plucky Irish winger is a perpetual-motion machine who seemingly never stops running. This season he has contributed a few goals as well. Might be tempting for someone looking to provide instant dynamism to their side.
48. Sebastien Puygrenier, 25, Nancy
He's ready for a bigger stage and if you want a giant, no-frills old school stopper who'll get to the ball first and boot it in Row Z, he's a sensible option.
47. Goran Pandev, 24, Lazio
A gifted and unselfish second striker who looks on the cusp of stardom. Lazio are notoriously cash-strapped and won't turn down a reasonable offer.
46. Tim Borowski, 27, Werder Bremen
This giant (6ft 5in) hyperactive midfielder gives you work rate and goals. He has 18 months left on his current deal and has had the odd run-in with his manager, Thomas Schaaf, which suggest he may be ready to up sticks.
45. Antonio Cassano, 25, Sampdoria (on loan from Real Madrid)
Approach this outrageously talented basket case with caution . . . but, if you can unlock his ability, you will find one of the most gifted players in Europe. Sampdoria have a buy-back option but a decent offer will pry him loose. A gamble but possibly a worthwhile one.
44. Willy Sagnol, 30, Bayern Munich
It's not often a veteran right back with 53 French caps becomes available but Sagnol says the rift with Ottmar Hitzfeld, the Bayern manager, can't be healed. Still has several seasons at the highest level in his 30-year-old legs.
43. Johan Elmander, 26, Toulouse
A late bloomer who really came into his own only in the past two years, Elmander is a big, athletic striker who probably still hasn't fully tapped into his talents. Toulouse are a selling club, and there is plenty of interest.
42. Miguel Veloso, 21, Sporting Lisbon
Tough-tackling holding midfielder in the Claude Makelele mould who can also line up as a defender. Veloso is calm, composed and reads the game uncannily well. Don't expect him to stick around past the summer.
41. Cristiano Lucarelli, 32, Shakhtar Donetsk
The veteran target man worked out a deal whereby Shakhtar will let him go on loan for the next six months, provided he returns for their 2008-09 Champions League campaign. If you're looking for a big, hulking goal machine on a short-term basis, he's your man.
40. Roysten Drenthe, 20, Real Madrid
Hyped to high heaven, he's been a bust at the Bernabeu. Too young to write off, though Real are willing to listen to offers. Given his ability, if he finds a club that can keep him on the straight and narrow, he could be an excellent signing.
39. Elano, 26, Manchester City
Everybody has his price and, despite having just arrived, plenty of clubs are lining up big money bids for the Brazilian maestro. Unless City prove to him they're ready to challenge for the title next season, he may push for a move.
38. Javier Saviola, 26, Real Madrid
Started for Argentina in the World Cup, but can't get a game at the Bernabeu after arriving on a free in the summer. Saviola is young enough to turn his career around and Real are happy to listen to offers. He's an expensive guy to have at the end of the bench.
37. Christopher Samba, 23, Blackburn Rovers
Despite a long-term contract, too many scouts are already salivating over the Rovers defender to believe he'll see it out. Arguably Mark Hughes's best signing, pound for pound.
36. Ricardo Quaresma, 24, Porto
Screwed up his chance at Barcelona, but has consistently been one of the best wingers in Europe since then. A mesmerising dribbler who also knows when to be unselfish, Porto will hold out for a big fee, but it's hard to see them hanging on to him.
35. Marco Amelia, 25, Livorno
Italy's No 2 goalkeeper is, incredibly, still stuck at a club mired in the relegation scrap year after year. Has been linked with a move for the past 18 months. Sooner or later it has to happen.
34. Vincent Kompany, 21, SV Hamburg
Injuries have limited his development somewhat, but he's big, strong, quick and bright: invaluable assets for a central defender. Could be one of those "below-the-radar" deals that reveals a hidden gem.
33. Luke Moore, 21, Aston Villa
He rejected a new deal last month and is out of contract in 2009, which suggests he's ripe for a move. Has slipped down the pecking order, but at his age, is definitely worth a look.
32. Mario Gomez, 22, VfB Stuttgart
Germany’s footballer of the year last season is a big, brawny centre forward with an eye for goal. Stuttgart would love to hang on to him for another season but, at the right price, they'll let him go.
31. Tiago, 26, Juventus
Hasn't really made the grade this season and Juventus are quietly listening to offers. The Portuguese midfielder could be a bargain for a number of clubs and, at his age, has a lot of good football left in him.
30. Olof Mellberg, 30, Aston Villa
Dependable, durable, physical and intelligent, Mellberg is on the market because he is out of contract in June. As Bosmans go, this one looks like a no-brainer for a hugely experienced defender with 79 Sweden caps and ten years’ experience in La Liga and the Premier League.
29. Joao Moutinho, 21, Sporting Lisbon
An eerily accurate passer and a natural leader who is already captaining Sporting despite his young age. Has plenty of drive and determination to go with his excellent technique and work rate.
28. Ever Banega, 19, Boca Juniors
Probably Argentina's brightest domestic starlet right now and arguably the best player at the Under-20 World Cup. Banega is a deep lying midfielder in the Andrea Pirlo mould who looks set for a big move to Europe.
27. Miguel Angel Angulo, 30, Valencia
Like Albelda, he has been shown the door at the Mestalla. Don't let that put you off, he's an intelligent and unselfish winger who can do a job for any top side. And, unlike others, he won't cry if he's not in the starting XI.
26. Mancini, 27, AS Roma
This tricky winger and step-over king has only 18 months left on his contract, which means he's ripe for someone to swoop in with an offer. One of the better wide men in Serie A, he has an uncanny ability to beat his man, which is always a prized asset.
25. Lassana Diarra, 22, Arsenal
A mystery wrapped in an enigma. Since the summer, he has featured as many times for France (seven) as he has for Arsenal in the Premier League. Given his age, it seems inevitable that someone will rescue from the Emirates before he gets too many splinters in his rear end.
24. Afonso Alves, 26, Heerenveen
Alves threw a hissy fit when he wasn't sold last summer and promises to produce another one if he doesn't get a move. The occasional tantrum, however, may be outweighed by his scoring record: 45 in 39 games since moving to Holland and seven in one game in October.
23. Peter Crouch, 26, Liverpool
Rafael Benitez says nice things about Crouch, but he doesn't get much love in terms of playing time. With a contract expiring in 18 months, he's ripe for a move, otherwise he'll be the elongated photo-negative version of Defoe: an England forward who can't start for his club side.
22. Jeremy Menez, 20, AS Monaco
Comparisons to Zinedine Zidane might be a bit blasphemous at this stage, but he has all the gifts to succeed. A tricky dribbler and natural playmaker, he's also a regular goalscorer who can feature up front. Oh, and he's on the record saying he "dreams of Arsenal".
21. Cristian Zapata, 21, Udinese
The best defender you've (probably) never heard of. Quiet, unassuming but a fearsome athlete with size, strength and pace, he has been a Serie A starter since he was a teenager. Think a younger Sol Campbell, only less complicated.
20. Jens Lehmann, 38, Arsenal
OK, so he was born in the 1960s and has lost his starting place at Arsenal. But it wasn't that long ago that he was superlative in leading Germany to the World Cup semi-finals, and he'll be available on a free in June. Does nobody fancy a punt?
19. Jermain Defoe, 25, Tottenham Hotspur
Amazingly, he has started only one Premier League game this season. In the past three and a half seasons, he has scored 35 league goals, while making only 71 starts. With his contract expiring in 2009 (and no sign of a deal on the horizon) he's ready to move on.
18. Deco, 30, Barcelona
Probably should have moved last summer, but remains available at the right price. A natural playmaker who, in the right context, holds his own defensively as well, he'd upgrade almost any midfield.
17. Giles Barnes, 19, Derby County
No, we haven't really seen what he can do in the Premier League, but Derby are likely to go down and he doesn't need a year of slogging it out in the Championship. He brings technique, creativity and improvisation, all qualities English youngsters supposedly lack.
16. Amauri, 27, Palermo
The poor man's Adriano (without the boozing and the flab). Amauri is a big, strong and mobile target man who puts the team first and never stops running. Now that he has an EU passport, he's a very tradeable commodity.
15. Rafael Van der Vaart, 24, SV Hamburg
After being billed as the second coming as a teenager, he has taken a few years to settle down, but is now comfortably one of the better attacking midfielders around. Already has 50 Dutch caps.
14 Nicolas Anelka, 28, Bolton Wanderers
Have boots, will travel. Seven moves in his career will soon become eight, which makes sense for a consistent centre forward who has reached double figures in league goals in each of the past six seasons.
13. Alan Hutton, 23, Rangers
A natural attacking full back who is ironing out some of his defensive kinks, Hutton may be the best British wide defender right now. If he wants a move, it will be very hard for Rangers to hang on to him.
12. David Albelda, 30, Valencia
His manager has blamed him for Valencia's ills and dropped him, which effectively means he's up for sale (and for a reasonable price, too). It's not often a guy his age with 50 Spanish caps goes on the market.
11. Adriano, 25, Sao Paulo (on loan from Inter Milan)
Yes, he's had weight and alcohol problems and Inter have shipped him home to Brazil so that he can regain his mojo. He's a gamble by any estimation but, given his age and that he is potentially one of the most feared centre forwards around, it may be a worthwhile one.
10. Urby Emanuelson 21, Ajax
Classic attacking full back who brings width and trickery to the left flank. Ajax don't really want to lose both him and Maduro, but they may well have no choice if the right offer comes in.
9. Didier Drogba, 29, Chelsea
He's under contract until 2010, but makes no secret of the fact that he wants to keep his options open and see how things go under Avram Grant. If Chelsea can get the right price, selling him might be the kind of move that benefits all parties.
8. Diego, 22, Werder Bremen
He flopped as a teenager at Porto but, in the past two years, he has established himself as one of the best playmaking attacking midfielders in Europe. Creates tons of chances and scores a fair few, too.
7. Gianluza Zambrotta, 30, Barcelona
The prototypical modern full back who can fill either flank, he's been in and out at the Nou Camp this season. With the manager's future undecided, he could be tempted to try his luck elsewhere.
6. Frank Lampard, 29, Chelsea
It all depends on whether he extends his contract at Stamford Bridge, which expires in June 2009. He said he'll make a decision at the end of the season and, if no deal is reached, look for him to seek employment elsewhere.
5. Luka Modric, 22, Dinamo Zagreb
Despite his age, he bosses games from his perch in central midfield. Great personality and leadership and chips in with a fair few goals as well. Premier League be warned: Dinamo are looking for a big pay day.
4. Hedwiges Maduro, 22, Ajax
A high-energy sparkplug in the middle of the park, Maduro is the kind of guy managers love. Other clubs love that he has refused a contract extension and can move on a free in June even more. Don't expect him to last that long.
3. Karim Benzema, 20, Lyons
The price tag will be high given his age but, if he continues to progress, it will only get steeper. Quick, accurate and blessed with loads of personality, he's the next big thing coming out of French football.
2. Dimitar Berbatov, 26, Tottenham Hotspur
Very gifted and prolific, he often leaves you with the sense that there's more to come. Spurs may want to cash in, especially since they are a year or two from contending. Plus, if he doesn't want to be there, why keep him around?
1. Ronaldinho, 27, Barcelona
Of course, he'll cost a mint - both in wages and transfer fee - and you may have bought into the idea that his career is on the wane. Don't believe the haters. He's got 46 goals in his past 71 Liga starts . . . and he's not even a goalscorer!
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Are there any players on the list that you would want your manager to sign?