Liverpool manager Jurgen Klopp is convinced that a concussion hampered the performance of goalkeeper Loris Karius during his side's 3-1 loss to Real Madrid in May's Champions League Final.

In early June, a scan at Boston General Hospital revealed that Karius had incurred a concussion during the match, likely when he appeared to have been struck by an elbow from Real defender Sergio Ramos just before Karim Benzema's first goal in the 51st minute. Both goals scored by Benzema during the match were the results of gaffes from Karius.

"We don't use it as an excuse, we use it as an explanation," said Klopp. "For me, it is 100 per cent the explanation [for his performance]. He was influenced by that knock - that is 100 per cent."

Klopp said, at the time, the idea that his 'keeper might be concussed never crossed his mind, but was contacted by Germany and Bayern legend Franz Beckenbauer, who was told by a doctor that Karius appeared to have picked up a head injury.

"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?'" Klopp said.

After finishing runners up in the Champions League and in fourth spot in the Premier League last season, the Reds' preseason gets underway on Saturday with a friendly versus sixth-division side Chester in which Karius is expected to feature.

"If you ask Loris, he says he didn't think about it and didn't use it for a second as an excuse," Klopp said of his 'keeper, who he insists has moved on from the Final. "From this point of view, from my side everything is fine. We don't think about that any more and we start completely new."

Liverpool kick off their Premier League campaign on August 12 when they host West Ham at Anfield.