How does he fit into this team? From what I saw in his appearance today, he was basically just existing around the centre of the pitch. Now, I'll give him that he's just come back from injury, and I shouldn't expect huge things from him this early on, but I struggle to see what he's going to bring to this current United formation. You've got a midfield three of Valencia - Blind - Di Maria, and he replaced Valencia. Valencia, today, was playing the role that we usually look to Herrera to play, that combination CM/RM which requires a lot of running due to one of the key responsibilities being to drift out to the wing, support the full-back, and play crosses in. Does Fellaini have the energy, pace and crossing ability to do this? I don't think so.
The other alternative is to put him in where Blind played, but then I don't think Fellaini offers an improvement on Blind's passing and tackling in that defensive midfield role, and if you do that then you have to push Blind out to one of those wider midfield positions, where he may well struggle.