The deadly Dutchman has scored 23 goals in 23 starts.
Geordie Carrick said: "We knew he was a top player because we played against him. But playing with him and seeing him in training, he's better than I thought he was.
"To make such an impact at this club straight away speaks volumes, not only about how good he is but about his attitude, personality and character.
"It is a huge bar here and I think for each player who comes through the doors at United, when you sign you embrace what is going on and the philosophy of the club.
"The respect that all the lads have for the club, even the likes of Scholesy and Giggsy, is incredible within the players.
"That's down to the continuity of the squad and the philosophy and application of everyone with that amazing desire to win."