Helping the Blues win two titles in three years, Matic was an influential and popular figure at Stamford Bridge but was surprisingly allowed to join United in July.
The 29-year-old took little time to adapt to his new surroundings and has put in a string of assured performances this season to help United go through August and September unbeaten.
Wilkins insists he has ‘no idea’ why Chelsea sanctioned his departure and says Matic has allowed his new teammates to come into their own.
Speaking on Sky Sports, the former Blues coach said: ‘Why did Chelsea sell him at £40million?
‘I’ve no idea, I really hate no idea whatsoever. This guy has been an absolute revelation at Manchester United.
‘He’s allowing everybody to do their jobs and do their jobs a lot better. His stature is at six-foot four and he just allows people to do their job.’
Wilkins, who was Chelsea’s assistant manager as recent as 2010, added: ‘As far as I’m concerned we should never have allowed him to leave.
‘You’ve now got a Michael Carrick with legs. Michael I still think can come in and do a job for Manchester United and he probably will do as the season progresses.
‘But Matic, Mourinho could not have got a better player to sit in front of that back four.’