Premier League clubs will be on high alert over the next six months and more with some top names seeing their contract run out in the summer of 2021.
These players are free to talk to clubs from foreign leagues from January 1, as their current clubs weigh up whether to offer a new deal, sell for a reduced fee in January, or allow to leave on a free in the summer.
The pool of out-of-contract players is more high profile than ever, with club legends in Lionel Messi and Sergio Aguero up for grabs if they do not sign a new deal.
Lionel Messi (Barcelona)
The wheels on the Messi saga have started to turn again.
His non-exit from Barcelona in the summer dominated headlines for a couple of weeks, but a new contract has not been signed; Messi's deal at the Nou Camp still runs out this summer, where his desire to leave on a free will not need to go through any lawyers.
Where will it be next for the superstar? Manchester City and PSG will be among the favourites, but could he make a move back to Argentina with childhood club Newell's Old Boys - or instead to another continent?
The latest is that Messi has said he will make a decision over his Barcelona future at the end of the season.
While he refused to be drawn on his potential next destination in an interview with Spanish TV station La Sexta, Messi did speak of his close friendship with Paris Saint-Germain forward Neymar, and said he would one day like to play in Major League Soccer.
Will seeds be sown in January over his next move? Watch this space.
Sergio Aguero (Man City)
Next summer will mark a decade since Aguero joined City from Atletico Madrid, but it may well be 10 years and out for the 32-year-old.
In 2015, Aguero said he would move to Independiente in 2019 when his then-contract expired, and that move to Argentina could be on the cards again this summer.
Aguero has struggled with injuries this season and City, without him, have lacked a cutting edge, but a conclusion to the forward's contract situation has not yet been reached.
Pep Guardiola appears to remain convinced that Gabriel Jesus is capable of being Aguero's long-term successor and the Manchester City boss has played down the chances of extra attacking reinforcements arriving in January.
David Alaba (Bayern Munich)
Liverpool and Manchester City are interested in David Alaba - but the Premier League pair look set to be frustrated as it stands.
Bayern president Herbert Hainer recently told Bayerischer Rundfunk that negotiations over a new deal for Alaba had ceased, with the player now in the final year of his current contract.
A source close to the player told Sky Sports News: "David is not considering any other clubs at this stage. He is focussing a hundred per cent on Bayern."
Despite his ongoing public contract dispute with Bayern, the Austria international plans to remain at the Allianz Arena until the end of this season.
But with Inter Milan, Real Madrid, Paris Saint-Germain and Juventus also understood to be keen on signing the 28-year old, expect another scramble for his signature before too long.
Mesut Ozil (Arsenal)
That £350,000-a-week contract in 2018 continues to look very expensive for Arsenal right now, with Ozil getting no playing time and seemingly not in a rush to leave the Emirates.
His contract is up in the summer, and the 31-year-old will surely be on his way, with no shortage of clubs, but seemingly not many willing to match his huge wage demands.
Ozil has not played for Mikel Arteta's side since March 7 and was not included in the Arsenal's squads for the Premier League or Europa League.
Arteta has shown little inclination to change his mind over the former Germany international but Ozil says he continues to hope he will get a chance to help his struggling team-mates.
What will give?
Memphis Depay (Lyon)
Contract talk surrounding the former Manchester United man has quietened since before the summer, with the 26-year-old linked with a move to Barcelona.
That has not materialised, but Depay, who has worked with Barca head coach Ronald Koeman in the Dutch national side, should be on the move in January or the summer.
"I'm 26 and almost free, so you can expect clubs to be interested in me, no?" he said recently, and he's probably right.
Koeman has gone public with his interest, describing Depay in October as "a great player" though reports in Spain have suggested the Barca boss may be inclined to strengthen elsewhere first.
Gini Wijnaldum (Liverpool)
Another Dutchman heavily linked with Barcelona is Liverpool's title-winning midfielder Wijnaldum.
Koeman remains hopeful he can persuade his fellow Dutchman to turn down a new contract offer from Liverpool and join him at the Nou Camp.
But Jurgen Klopp remains keen on convincing Wijnaldum to stay on Merseyside.
The player has told Liverpool he will give them his answer imminently.
Arkadiusz Milik (Napoli)
Heavily linked with Tottenham and Everton, striker Milik stayed at Napoli this summer, but should leave at the first attempt possible in January.
He was even left out of Gennaro Gattuso's Napoli squad for the rest of the season, despite having scored 34 goals in his last two campaigns.
"We'll see where I go. At this point, I am not with anyone," Milik said recently. "Now, I'll wait for the next transfer window and I hope the clubs can find an understanding."
Angel Di Maria should be on his way out of PSG in January or next summer, saying recently he hopes PSG will be his "last club in Europe". while team-mate Julian Draxler could not seal a summer move away despite being linked with Leeds and Hertha Berlin.
Also notably out of contract in 2021 are Sergio Ramos (Real Madrid), Jerome Boateng (Bayern Munich), Gianluigi Donnarumma (AC Milan), Diego Costa (Atletico Madrid), Jesse Lingard (Man Utd), Shkodran Mustafi (Arsenal), Eric Garcia (Man City) and Florian Thauvin (Marseille).
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