Jose Mourinho has revealed his concern at the potential extent of the knee injury sustained by Manchester United defender Eric Bailly.

The centre-back has been the club's mainstay in the back-four so far this season with the Ivorian internationally mostly impressing during his early weeks at the club since signing from Villarreal.

He was named Man United Player of the Month for August.

But the 22-year-old was forced to limp on 52 minutes with a knee problem during United's 4-0 defeat to Chelsea at Stamford Bridge on Sunday afternoon. 

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He was replaced by Marcos Rojo for the remainder of the second half. 

And the injury could keep him out for a lengthy period with Mourinho describing it as "really bad".

"He is injured and I am afraid he is badly injured. In his knee, in the ligament area. He feels that it is really bad," said the Man United manager after the match.