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.
Arsenal defeated London rivals Chelsea 1-0 for their first win in four Premier League games on Sunday as a headed goal by stand-in striker Mikel Merino boosted their faint hopes of catching up with runaway leaders Liverpool.
Carlos Alcaraz's hopes of capturing a third successive Indian Wells title went up in smoke on Saturday and the Spaniard said his inability to tame his nerves was more of a disappointment than the stunning semi-final defeat by Jack Draper.
McLaren's Lando Norris swept to victory in a wet and wild Australian Grand Prix on Sunday, holding off defending champion Max Verstappen in a white-knuckle finish to a Formula One season-opener littered with crashes and safety cars.
Manchester City could only muster a 2-2 Premier League draw with Brighton & Hove Albion on Saturday, dropping points in a blow to their hopes of playing European football next season.
After struggling with setup issues through Australian Grand Prix practice, Max Verstappen was surprised by his Red Bull car's performance on Saturday as the Formula One defending champion took third place in qualifying for the season-opening race.