3. Paul Pogba, Juventus
This is always labelled as the great mistake by the 13-time Premier League champions as Pogba left for Juve on a free in 2012 and is now regarded as one of the best midfielders in the world aged just 21-years-old.
Yet in truth the club wanted to keep him, but the France international wanted to move on and he has certainly developed better in Serie A then he was ever likely to in England.