The Germany international was culpable for two of Los Blancos' goals in the 3-1 win for the La Liga side, first rolling the ball straight to Karim Benzema and then letting Gareth Bale's strike from distance squirm through his hands.
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.
Speaking about the incident, Klopp believes Karius' performance was inhibited from that point on, per BBC Sport.
"For me, it is 100 per cent the explanation [for his performance]," said Klopp. "He was influenced by that knock, that is 100 per cent."
As relayed by David Maddock of the Daily Mirror, the Liverpool manager said it was Germany icon Franz Beckenbauer who relayed information from a German doctor back to him suggesting Karius may have been concussed:
David Maddock @MaddockMirror
Klopp: “4 days after the final Beckenbauer called me and said ‘your goalkeeper had a concussion’ I saw it and thought how can we all think the boy who didn’t show any weakness in that game until then made these big mistakes and nobody thinks it’s because of the knock he got?"#LFC
The support of the stopper from the Liverpool chief comes a day after it was reported that the Anfield club are ready to back him as their No. 1 next season.
According to Maddock, the Reds are set to miss out on key targets at the base of the team, with Atletico Madrid's Jan Oblak and Roma's Alisson Becker proving to be too costly.
Paul Joyce of The Times has said the Reds have been trying to add a new goalkeeper, as noted by Rob Gutmann on Twitter:
For Karius, it's a huge opportunity after a galling night in his career, as the game was on a knife edge before the aforementioned incidents in the second period.
Earlier in the season, the German had taken over from Simon Mignolet as the starting goalkeeper and had done well in the main. While there are still weaknesses in his game, football writer Jack Lusby suggested there aren't many major upgrades available:
Regardless of what happened in the final, there are reservations about Karius, especially when all other areas of the Liverpool squad appear to be in excellent shape ahead of the 2018-19 season. If the Reds are to challenge for top honours, you feel a big injection of quality is needed between the sticks.
Karius will be hoping to show he can be that man, and it's clear Klopp is ready to back the goalkeeper ahead of the new season. Still, overcoming such a devastating game in Kiev will be a massive challenge for the stopper, whether his performance was hindered by concussion or not.