#3 Ousmane Dembele
One of several players identified as deadwood at Barcelona in the summer, Ousmane Dembele was on the cusp of joining Manchester United, but the move didn't materialise.
Despite not being in the plans of Ronald Koeman, the player stayed back at the Camp Nou and sought to work his way into the manager's preferred starting XI.
The Frenchman has scored twice in La Liga and three times in the Champions League this season but has largely been a pale shadow of the player that lit up Borussia Dortmund during his Bundesliga stint.
With Manchester United failing to land their number one target Jadon Sancho in the summer and unlikely to do so in January as well, Dembele has emerged as a viable alternative.
#2 Papu Gomez
Papu Gomez has been a key player for Atalanta since joining the Serie A club in the summer of 2014. However, with the player reportedly experiencing a relationship breakdown with his club coach, he could leave Atalanta in January.
Gomez has had goal-scoring contributions aplenty for Atalanta in recent times - he scored 14 times and assisted 27 in the last two Serie A seasons - but has found game-time relatively difficult to come by this season.
Italian giants Juventus are reportedly interested in the services of Gomez. The Bianconeri have a history of swooping up the best players of their domestic rivals and could do so with Atalanta as well.
#1 Diego Costa
Diego Costa has found limited joy since returning to Atletico Madrid after a fairly successful stint with Chelsea.
The Spaniard, who has terminated his contract with the Rojiblancos, could still flourish at another club despite his diminishing returns in recent times.
The 32-year-old has no dearth of suitors, with struggling Arsenal emerging as one of several contenders for Costa's services. However, it remains to be seen if the player opts to go back to the Premier League or move to another La Liga club in the upcoming January transfer window.