Wilkins told talkSPORT that he feels the England man could boost United's title bid.
"He was fantastic [against Everton], wasn't he?" said Wilkins. "In the 11 games he's played, he's got six goals already.
"This is the club's decision to let him go - it's nothing to do with Rafa Benitez - and in my opinion it's the wrong decision. You need these older players to show the youngsters what it means to play for Chelsea."
He added: "He'll cost nothing, he's about four years younger than Giggs and Scholes and he scores goals from midfield. He's scored more goals this year than Carrick, Cleverley and Scholes combined.
"He's comfortably got two or three more seasons in him. He won't play 90 minutes every week but if he starts 20 games for Man United he'll score them seven goals."