Karius gifted Real Madrid two goals during Liverpool’s 3-1 defeat by the European champions, having beforehand sustained an elbow to the head by Sergio Ramos.
For Madrid’s first, the German threw the ball into the path of Karim Benzema inside his own area before later parrying Gareth Bale’s shot into the back his net for Los Blancos’ third.
Karis subsequently underwent scans at Massachusetts General Hospital in Boston. The hospital’s head injury specialist, Dr Ross Zafonte, said in a statement that the concussion “likely occurred immediately” following the second-half collision with Ramos.
Dr Zafonte added it was “possible” the injury “would affect [Karius’] performance”.
But Chelsea No 1 Courtois questioned the claims, alluding to the fact Karius made two impressive stops despite being concussed.
“It happened to me with Alexis Sanchez – I had a concussion and I couldn’t see the ball so after 20 minutes I went out of the game because I couldn’t see the ball,” Courtois said during Belgium’s media day.
“I feel sorry for what happened with him, but to blame it on concussion that he made those mistakes – he also made two amazing saves. So that was luck then? I don’t know because he couldn’t see the ball.
“It’s unfortunate for him to have made those mistakes but if you have concussion you will leave the game or the doctors will tell you look you cannot see clearly anymore you must leave the game.
“If they want to say it’s because of that, it’s OK. He said after the game he made two mistakes, I think everyone will accept that.
“It can happen as a goalkeeper but to blame it on a concussion now, I find it strange. But if medics says that from Boston it’s OK.”