#4 David Luiz (Chelsea to Arsenal)
The Brazilian was an important part of Chelsea's title-winning campaign last season but has been shockingly frozen out this season.
After starting out injured, Antonio Conte has continued with his faith in youngster Andreas Christensen, who has performed admirably considering his age and has done nothing wrong to be relegated to the bench again.
Luiz is too good a player to leave off the pitch, however. He returned to the club from PSG a much better defender, having cut out the needless mistakes that were a feature of his game in his first spell at Stamford Bridge.
Commanding, confident, and skillful with the ball at his feet, he'll have suitors all over Europe looking for him. He shouldn't have to look too far for a move: London rivals Arsenal are in desperate need of a world-class defender and have been for some time now.
The club has too often been let down by their weak defense. Players like Mesut Ozil and Alexis Sanchez have delivered at the other end of the field, but Arsenal's centre-backs have been exposed game after game.
Per Mertesacker and Shkodran Mustafi are too slow and hesitant, something Luiz definitely isn't. His strong presence in the back line would immediately enable Arsenal to be tighter and more compact and it'd be likely that he'd improve the performances of players like Hector Bellerin and Mustafi around him.
At 30 years old, he likely wouldn't be too expensive. Arsene Wenger needs to accept when he needs a player and get Luiz to save their struggling season.