Chelsea sold Matic to United for £40m despite playing an integral part in last season’s title win.
The Serbian has excelled for Jose Mourinho‘s side so far this season and Wilkins cannot believe that the Blues helped strengthen their rival.
“It’s the worst I’ve ever seen, if I can say. I cannot see that for the life of me.
“You’ve got a guy here who was so paramount to Chelsea along with [N’Golo] Kante in the middle of the pitch, winning the championship for Chelsea the year before and all of a sudden you’ve sold him to one of or the biggest rival we have.
“I say we because I am a Chelsea supporter so I’m speaking from the heart when I speak.
“I just could not see why we would let Nemanja go there. He’s been outstanding for us and you’ve seen in the short period that he’s been there, how he’s allowed [Paul] Pogba to basically go and do what he wants.
“I just couldn’t see that piece of business, at all.”