Manchester United defender Eric Bailly fears he has suffered a "really bad" knee ligament injury, according to Jose Mourinho.
The centre-back was hurt tangling with Eden Hazard early into the second half and was taken off after 52 minutes of United's 4-0 defeat to Chelsea at Stamford Bridge.
Mourinho confirmed: "He is injured and I am afraid it is a bad injury. It is in his knee, the ligament area. He feels it is really bad."
The injury comes as a further, sizable blow to Mourinho after he and his side were humiliated on his first return to Stamford Bridge.
Bailly has been in excellent form since his summer move from Villarreal and, after Mourinho blamed a string of individual defensive errors for United's heavy defeat, Bailly's loss is sure to be felt.
United are already without Phil Jones with a knee ligament injury, while Chris Smalling has only just recovered from a muscle problem.
Wayne Rooney also missed the trip to West London with a muscle injury picked up in training on Friday.