Palace manager Oliver Glasner confirmed Mateta had suffered a serious injury to his ear but said the impact could have ended the Frenchman’s career.
“Just imagine, if he hits his face straight, with his power, with the studs – it is the end of JP’s career,” said Glasner.
“I’m pretty sure he didn’t want to injure JP in this situation, but I also think that you have to decide when you make such an impact, you just can’t do it in this way.”
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.
Palace chairman Steve Parish described it as the “most reckless challenge” he had ever seen.
“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 his life, with a challenge like that.”
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’ resistance 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 ensure progress when Eddie Nketiah’s looping header found the far corner.
