I would say that in addition to Fellaini not really fitting in overall (he's not going to play as an attacking midfielder with Rooney and Kagawa capable of playing off of RVP), he just doesn't mesh well playing alongside Carrick.
Carrick's a fantastic player, but if he's lacking in one thing it's mobility (makes up for it with positioning), so it's not a great fit to play Fellaini next to him, considering Fellaini's slow as shite (and obviously not the most technical player). It's just a midfield two that's really really lacking in mobility.
Strootman or Paulinho would have been a much better fit.
This post was edited on 12/8 at 8:42 am