The German was roundly criticised for his performance during the 3-1 loss in Kiev after two calamitous errors led to the Blancos securing a third successive European title.
But tests carried out by the Massachusetts General Hospital have now found that Karius was suffering from a head injury at the time.
"On May 31, 2018 Mr. Karius underwent a comprehensive examination by Dr. Ross Zafonte and Dr. Lenore Herget in Boston at Massachusetts General Hospital and Spaulding Rehabilitation Hospital," a statement read.
"After carefully reviewing game film and integrating a detailed history – including his reported present and immediate post-contact subjective symptoms – physical examination and objective metrics, we have concluded that Mr. Karius sustained a concussion during the match May 26, 2018.
"At the time of our evaluation, Mr. Karius’s principal residual symptoms and objective signs suggested that visual spatial dysfunction existed and likely occurred immediately following the event. Additional symptomatic and objectively noted areas of dysfunction also persisted. It could be possible that such deficits would affect performance.
"We also note that Mr. Karius has reported significant and steady improvement since the concussive event, and we expect him to make a full recovery based on the results of the examination. We expect that with treatment and by following prescribed activity protocols he will continue to improve. We have encouraged vigilance and an emphasis on safety in his eventual return to full activity."
Though not confirmed by the statement, there is a suggestion that the injury that Karius suffered came due to challenge from Madrid captain Sergio Ramos, who had earlier instigated the first-half challenge that saw Mohamed Salah suffer a dislocated shoulder.
Early in the second period the pair were involved a coming together inside the penalty area, with replays showing Karius was caught by the elbow of the Spain international defender.
Though clearly shaken by the incident, Karius was able to continue without treatment, with the referee also opting not to award a foul.
Moments later the ball was in the back of the Liverpool net as Karius looked to roll the ball out to a team-mate, only for Karim Benzema to block the ball and divert it into the bottom corner.
Though Karius had no chance of stopping Gareth Bale's stunning overhead kick to make it 2-1 following Sadio Mane's equaliser, his night to forget continued in the closing stages as he spilled a speculative drive from the Welshman into his own net.
Though Karius apologised to his team-mates and supporters after full-time, many have questioned whether he should play for the club again, with Roma's Alisson a reported target to replace him next season.
But these latest results may soften those views as he looks to rebuild his career at the age of 24.
Karius himself asked for the results of the tests to be revealed, with Liverpool themselves offering no objections having not being involved in the process.