Kurt Zouma was left screaming on the floor in agony after picking up what looked to be a season-ending injury against Manchester United.
The defender landed awkwardly on his knee, which then buckled, while challenging for the ball with Juan Mata. The French international was replaced by Gary Cahill.
"Kurt Zouma is in trouble. He's screaming. He jumped so high and he fell awkwardly - his knee went the wrong way. It should be ahead of you, not behind you," said former Liverpool midfielder Danny Murphy, who was commentating on the game for BBC Five Live.
"It's one of the worst sights in football, seeing somebody on the pitch with an injury like that."
The injury to Zouma, which comes days after fellow centre-back John Terry confirmed he would be leaving the club at the end of the season, was a low point in an underwhelming day at the office for Chelsea.
Guus Hiddink's side fell behind against the Red Devils thanks to a Jesse Lingard goal and it looked as though some goalkeeping heroics from David de Gea had earned all three points for the away side.
However Diego Costa salvaged a point for the Blues in extra time, and the Spanish international was denied the chance to snatch all three points at the death by another superb De Gea save.
The result means Manchester United have slipped back in the race for the top four on a weekend when Arsenal, Leicester and Tottenham all won, while Chelsea are 11 points adrift of Louis van Gaal's side.