The German stopper subsequently underwent scans at Boston's Massachusetts General Hospital in the United States and was found to have been concussed during the second half of the match.
Courtois, speaking from his own experience, has claimed that he does not understand how Karius could have played on, and pointed out that his counterpart made two good saves after suffering concussion.
"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, speaking at Belgium's media day ahead of the World Cup, told reporters.
"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 any more you must leave the game.
"If they want to say it's because of that, it's okay. 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 say that from Boston it's okay."
Karius, who missed out on a place in Germany's World Cup squad, apologised to Liverpool supporters for his mistakes in the final.