The Serbian swapped Stamford Bridge for Old Trafford in July in a £40m (€43.6, $52.1m) deal, which saw him reunited with Jose Mourinho. Matic has hit the ground running in Manchester, playing a major role as United clinched three wins in as many games in the opening weeks of the campaign, while his former manager Antonio Conte was left regretting Chelsea's decision to let Matic go.
While some suggested United paid over the odds for the Serbia international, who turned 29 two weeks before the start of the campaign, most observers were left baffled by Chelsea's willingness to sell one of their key players to a direct Premier League rival.
Wilkins, who spent two seasons as assistant manager at Stamford Bridge under Carlo Ancelotti after a six-year playing career at the club, was particularly scathing of the move.
"It's the worst I've ever seen, if I can say," he told Sky Sports. "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 with 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."
While Matic has helped United to keep three clean sheets in as many games and already looks to be one of the best signings of the transfer window, Chelsea were left scrambling in the transfer window and ended up paying £35m for former Leicester City midfielder Danny Drinkwater.
However, Wilkins warned the former Manchester United youth star to stay away from Stamford Bridge, where his chances of regular game-time might be slim.
N'Golo Kante, Tiemoue Bakayoko and Cesc Fabregas are all vying for a starting position under Conte, and Wilkins does not think Drinkwater will be able to leapfrog the esteemed trio and secure a regular starting position at Chelsea.
"Danny [Drinkwater] has done really well for Leicester over the last couple of years. The important thing for him is to play," Wilkins told talkSPORT.
"Tiemoue Bakayoko cost £40m this summer, N'Golo Kante is a player everybody loves and with Cesc Fabregas there as well, is Danny Drinkwater going to get a game?
"If I was Danny, I'd be somewhere I could play, personally."