Fellaini signed for the Reds on transfer deadline day to finally link up with his former Everton manager David Moyes following a summer of speculation.
"He's got great potential, and if he's consistent with his best level, he will be a fantastic signing," Berg told MUTV. "He can play so play different positions, he's a good footballer but there's something about him. He can get players around him, he can control and dominate games, and I think United have too few players who can do that. That's why I think he will be a great signing.
"He's very difficult to handle in the box, but he's got that presence and that mentality that makes sure he stands out and does that little bit extra. It's not so much about technique and technical things, but he can score and set up goals. He's more like an English-type, not like a foreign player who can dominate with skills and tricks, but I think playing with better players will suit him.
"I just hope he doesn't play central midfield, I hope he can play up front next to van Persie, as a link up player and goal-scorer."
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