Manchester United defender Eric Bailly had to be carried off on a stretcher wearing a neck brace following a clash of heads with team-mate Harry Maguire during the first half of their FA Cup semi-final against Chelsea at Wembley.
The Ivory Coast international was left with blood pouring from a head wound after colliding with fellow defender Maguire in the closing stages of the first half.
He initially appeared to recover and got to his feet, but quickly laid back down on the pitch.
After several minutes of treatment from the Man Utd medical team, which included placing him in a neck brace, Bailly was taken off the pitch and down the tunnel on a stretcher.
The 26-year-old had already suffered a blow to the head minutes earlier when he attempted to beat Kurt Zouma to a Chelsea left-wing cross.
Maguire also needed treatment after the incident, but was able to continue with a bandage wrapped around his head.
Anthony Martial came on to replace Bailly, as manager Ole Gunnar Solskjaer switched back to his usual 4-3-2-1 formation having begun the match with three centre-backs in a 3-4-3 set up.
Even if Bailly escapes serious injury he is unlikely to feature in Manchester United's final two Premier League matches of the season because of the Premier League's concussion protocols, which has minimum recovery period of six days imposed from the time of the injury.
Man Utd will hope that the former Villarreal defender will be cleared in time for the resumption of their Europa League campaign, with the second leg of their round of 16 clash with LASK scheduled to take place on August 5.
The lengthy stoppage meant there were 11 minutes of time added on at the end of the first half, with Chelsea taking full advantage of the added time by taking the lead through Olivier Giroud, who met Cesar Azpilicueta's cross to flick the ball beyond David de Gea at his near post.
Things would get worse for Solskjaer's side just seconds into the second half, with Mason Mount's tame long-range effort squirming beyond De Gea to double Chelsea's advantage.