Millwall goalkeeper Liam Roberts made contact with Mateta following his horror kung-fu kick in their FA Cup clash this weekend which left the Frenchman with a "severe laceration" to his left ear which needed 25 stiches. Oliver Glasner told BBC Sport after the game that this tackle is absolutely unacceptable even if the intention was to go for the ball.
"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.
"We are not really happy. We can't be really happy. Of course it's a great win and we are into the quarter-finals, but when you lose a player, especially with a foul like this, you have two different feelings in your stomach."
"Honestly, I didn't want to see it. I just watched it and it's terrible. I'm sure the goalkeeper didn't want to injure JP in this situation, no player wants this. But if you get to the ball with this intensity, with the foot at this height, you cannot do that. It's so dangerous and we all have responsibilities for our health.
"I don't want to blame him (Roberts), but it is a terrible foul. I didn't see it in the game, it was so quick. I could see the goalkeeper had a lot of intensity, but he touched the ball first. I have seen it now in slow motion, and it is worse.”
It is understood the 27-year-old had no ill feeling towards the Millwall keeper and they wished each other well after the game. He will miss Palace's game against Ipswich Town on Saturday but could return after the international break when they face Fulham in the FA Cup.