Crystal Palace chairman Steve Parish branded the challenge by Millwall goalkeeper Liam Roberts that left Jean Philippe-Mateta in hospital as "the most reckless" he has ever seen.
Roberts was sent-off just eight minutes into Saturday's FA Cup fifth round tie, which Palace won 3-1, after catching Mateta's head with his boot as he raced out to clear the ball.
Referee Michael Oliver only issued a red card after a VAR review.
Mateta received lengthy treatment, including oxygen, on the pitch before being stretchered to an ambulance and transported to hospital.
"What we know, he's got a bad gash behind his ear and a head injury. Obviously he's at the hospital. So, we hope for the best," Parish told the BBC.
"That is the most reckless challenge on a football pitch I think I've ever seen and I think he needs to have a long hard look at himself, that lad, because he's endangering a fellow professional, maybe in his life, with a challenge like that."
Palace manager Oliver Glasner confirmed Mateta is conscious but that he has suffered a serious injury to his ear.
"He is conscious and he is in hospital. His ear looks terrible. It's a very serious injury so we hope all the best for him," said Glasner.
"We are not really happy, we can't be really happy. Of course, it's a great win and into the quarter-finals but when you lose a player, especially with a foul like this, you have two different feelings in your stomach."
Mateta had scored eight goals in his previous nine games and has 15 in total for Palace this season.
The 27-year-old also netted five times as France won silver at the Paris Olympics last year.
Parish drew comparisons to the famous clash between German goalkeeper Toni Schumacher and French forward Patrick Battiston at the 1982 World Cup.
"It's difficult for me to think about anything else at the moment with JP (Mateta) in hospital," added Parish.
"Somebody mentioned there was one in the World Cup in 1982 like it, but it's a dreadful challenge. And why the referee needed to go to the screen, I've got no idea."
Palace made use of the man advantage for virtually the whole game to book their place in the quarter-finals.
Japhet Tanganga's own goal broke the visitors resistence before Daniel Munoz prodded in a second.
Wes Harding pulled a goal back for the Lions, 13 minutes into first-half stoppage time added on for Mateta's treatment.
Palace were made to wait until 82 minutes to secure progress when Eddie Nketiah's looping header found the far corner.
Preston got the better of Burnley 3-0 in all-Championship tie to reach the quarter-finals for the first time since 1966 in another controversial clash.
The whole Burnley team refused to shake the hand of Preston forward Milutin Osmajic before kick-off after he was accused of making a racist comment towards Hannibal Mejbri when the sides met last month.
Mejbri was left out as Scott Parker made sweeping changes to his side, but Osmajic started and scored Preston's second goal, cupping his ear to the Burnley support in celebration.
Robbie Brady and Will Keane were also on target as Burnley's run of nine consecutive clean sheets came to an end.
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