The Belgium international completed a £27.5million move to be reunited with former Everton manager David Moyes at Old Trafford late on deadline day.
He has yet to make an appearance because of the international break but will be in the squad to face Crystal Palace at home on Saturday.
Much will be expected of the 25-year-old as he was Moyes' only significant signing of the summer after failed bids for Barcelona midfielder Cesc Fabregas, but Berg believes the Belgian can develop into a key figure for the side.
"He's got great potential and if he's consistent with his best level, he will be a fantastic signing," he told MUTV.
"He can play so many 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.
"I think with his passion and his mentality, he can make a big difference to United.
"He's not the kind of player to thread passes through but he has a sheer presence to hold the ball up, ability to win balls in the box and match-winning mentality - he raises his game for the big matches.
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