Midfield
United are spoilt for choice in the middle, but a closer look will reveal that the competition for the first team is between 5 players. This is because Mourinho likes a 3 man midfield and on current form and tactics, the players who are most likely to be shuffled around are Pereira, Herrera, Pogba, Matic and Fred.
However, the 3 man who will most likely make up the Manchester United midfield will be Paul Pogba, Nemanja Matic and Fred. Matic and Fred will most probably shoulder the lion's share of the defensive responsibilities, leaving Pogba free to join the attack and control the proceedings.
With the arrival of Fred, this season should be a breakthrough for the French World Cup winner. Last season, Pogba was strangled by Mourinho's defensive requirements, but with Fred likely to partner Matic as the deep-lying playmaker, Pogba should be looking ahead.
Also, Fred, as he showed in the preseason, can play at various positions in the middle, which should free even more space for Pogba to weave his magic.
In case of injuries, or if Mourinho wants to change things a bit, Pereira is more than capable to fill the deep-lying playmaker role and he and Fred did display the signs of a budding partnership during the preseason.
Ander Herrera is also another option, who can mix things up and perform a "job" as his manager demands. Additionally, McTominay and Fellaini also provide ample cover, abet not so much creatively. However, the Manchester United's strongest midfield this season should contain Fred, Matic and Pogba.