Manchester United defender Eric Bailly was wheeled off on a stretcher and wearing an oxygen mask after a second clash of heads during Sunday's FA Cup semi-final against Chelsea.
Bailly had returned to action after an aerial collision with Chelsea defender Kurt Zouma.
But there was another heavy blow to Bailly's head when he rose with teammate Harry Maguire to challenge Chelsea striker Olivier Giroud for the ball.
After concussion checks, Maguire was declared fit to continue with a bandage around his head.
But during a lengthy stoppage, Bailly staggered on the touchline before being placed on a stretcher and wheeled off the Wembley touchline on a stretcher by medical staff wearing protective clothing as part of coronavirus prevention measures.
"Eric is in hospital, going through all the routine checks and protocols. He got a cut in the back of his head as well so I don't really know any more. I haven't heard or spoken to the doctor about him," Manchester united manager Ole Gunnar Solskjaer told manutd.com.
"Of course that moment had a big, big impact on the game. Eric played very well in his 42 or 44 minutes that he was on for and we conceded just after the restart which was very disappointing.
"Eric was [until then] a big part of us not having any chances created against us really."
There was applause from the few people inside Wembley, where fans are locked out due to the pandemic.
During first-half stoppage time, Giroud gave Chelsea a 1-0 lead. United were beaten 3-1 as Chelsea will be returning to the national stadium on August 1 to face Arsenal in an all-London FA Cup final.
(With inputs from AP)