Number 3: Paul Pogba
Paul Pogba is the one who got away, and then came back for a then world record transfer fee, of course. There's always been a sense that Paul Pogba hasn't lived up to that enormous potential he showcased back at Juventus. In his favour though, he has often been asked to fulfill roles that he isn't most comfortable with, involving more defensive duties.
This could be his season, though. He's had an excellent World Cup, being an integral part of the victorious France squad. There's also the signing of Brazilian Fred, who offers a dynamic presence on the field, which could allow Pogba the freedom to roam further forward and influence the game like he used to at Juventus.
On his day, Pogba is definitely one of the best midfielders in the world and, if he can marshal the same form that he exhibited for France in the World Cup, Manchester United will definitely be genuine title contenders.