Kurt Zouma sustained what appeared to be a serious knee injury early in the second half of Chelsea's Premier League clash with Manchester United.
Zouma's right knee buckled as he landed after climbing unchallenged for a header just before the hour mark at Stamford Bridge.
The French defender's distress was audible as he lay on the ground, with players from both teams urging Chelsea's medical staff on to the pitch.
Zouma was then stretchered off, being replaced by Gary Cahill.
Jesse Lingard scored for United shortly after Zouma's departure, to put Louis van Gaal's team 1-0 up.