"He has attributes other people don't have. And with those qualities he has, I am sure he will be a big player for Manchester United."
The United boss is also pleased with the flexibility Fellaini brings, and is not committed to playing him in midfield all the time.
He added: "He can play higher up the field if we need him to, just behind a main striker.
"He can play as a defensive or holding midfield player. In fact he is comfortable in any position in the middle of the field.
"It was definitely a position where people would say we were short, not just of numbers, with the likes of Paul Scholes retiring and Darren Fletcher not being ready to come back just now. I am glad we have got him."