Karius made two errors that cost Liverpool dearly in the 3-1 defeat in Kiev, throwing the ball to Karim Benzema for Madrid's opening goal and spilling a shot from Gareth Bale for their third.
"The only thing I can say is he (Karius) had a concussion in the game", Klopp was quoted as saying by the club website.
"Now people could think for us it is the explanation - and for me it is 100 per cent the explanation and that's all".
Since the final, Karius had tests at a hospital in Boston where it was said he had suffered a concussion after an earlier clash when Liverpool defender Virgil van Dijk nudged Sergio Ramos into the goalkeeper early in the second half. "We do not use it as an excuse.Now people could think for us it is the explanation - and for me it is 100 per cent the explanation and that's all".
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"To be honest, it's not that I [spend] five hours on the line-up and think, "that will fit together".
He backed the keeper to make a fresh start in 2018-19, saying: "That's how it is".
"I got all the pictures from different perspectives, saw it and thought: 'How can we all think that the boy who didn't show any weakness in that game until then made these big mistakes in a very important game and nobody thinks it's because of the knock he got?'" If you make a mistake in a Champions League final, it's a mistake you can not change anymore, even if you want to - and we all want to. That's always important, that's what analysis should be: you explain why things happen.
"We need to cool down the whole situation and play football and work on our weaknesses, use our strengths and everything will be good".
Asked whether they could close the 25-point gulf to City, having been only one of two sides to beat them in the league, Gerrard added: "The million dollar question".