Crystal Palace forward Jean-Philippe Mateta was taken to hospital with a head injury after a collision with Millwall goalkeeper Liam Roberts early in their FA Cup fifth-round clash at Selhurst Park on Saturday.
Roberts was shown a red card, following a VAR review, after coming off his line to clear a long ball and catching the on-rushing Mateta in the head with his raised studs.
Frenchman Mateta, who has been in superb form for Premier League side Palace with 15 goals from 33 appearances, was given oxygen on the pitch during a lengthy stoppage before being taken off and put into an ambulance. He was replaced by Eddie Nketiah.
Speaking at halftime to the BBC, Palace chairman Steve Parish said Mateta had sustained a bad gash behind his ear and a head injury and was being assessed in hospital.
"Obviously, he's at the hospital, so we hope for the best. I mean there's a lot of emotion in football but we need to talk about that challenge. In all the time I've watched football, I've never seen a challenge like it.
"It is the most reckless challenge on a football pitch I think I've ever seen."
Palace were leading second-tier Millwall 2-1 at halftime.

Rohit and Kohli bid likely farewell to Australia as winners
Al Wahda defeats Al Dhafra, heads to quarter-finals of UAE President's Cup
Bencic battles past Kenin to set up Noskova final in Tokyo
Lionel Messi tallies twice as Inter Miami take opener vs. Nashville
