The Liverpool shot-stopper made two high-profile blunders as Real Madrid defeated the Reds 3-1 in Kiev, both coming after a collision with opposing centre-back Sergio Ramos, who seemed to hit him in the head.
On Monday, it was revealed that the 24-year-old had been seen by doctors in Boston, who had diagnosed him with concussion, which might explain his slips.
And the Chelsea man, who had been linked with a move to Jurgen Klopp’s side, admits that he does not find that a convincing explanation for the errors.
He told reporters: "I guess he got a blow on his head but 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.
"I feel sorry for what happened to him but to blame it on concussion now... in that space, that he made those mistakes he also made two amazing saves. Was that luck then, because he couldn't see the ball? I don't know.
"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 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."
Ramos, who was also involved in a tussle with Liverpool ace Mohamed Salah that resulted in the Egypt international going off injured, has mocked what he perceives as being the Reds’ excuses for defeat .
"After the goalkeeper said that I dazed him with a clash. I am only missing Firmino saying that he got a cold because a drop of my sweat landed on him," the centre-back said.
Chris Kirkland, meanwhile, told Goal that some of the criticisms of Karius have been unacceptable but feels the Reds are likely to still be in the market for a new goalkeeper in the summer .