Chelsea coach Ray Wilkins says his old club will regret allowing Nemanja Matic to leave for Manchester United.
Matic swapped Stamford Bridge for Old Trafford in July and has impressed in a red shirt.
"It's the worst [decision] I've ever seen, if I can say," Wilkins said on 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 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.
“I just could not see that for the life of me, why would we let Nemanja go there?"