Loris Karius was suffering from concussion when he committed the errors that gravely cost Liverpool in the Champions League final, experts have confirmed.

Medical professionals from the Massachusetts General Hospital examined goalkeeper Karius during his holiday in the United States and determined "visual spatial dysfunction" could have affected his much-criticised performance in Kiev.

Though the cause of the concussion was not speculated upon, Karius had collided with Real Madrid defender Sergio Ramos before gifting goals to Karim Benzema and Gareth Bale in the 3-1 loss.

Doctor Ross Zafonte and physical therapist Lenore Herget confirmed in a joint statement their belief the 24-year-old was feeling the effects of the head knock.

"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," the statement read.

"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."

The statement noted Karius, who after the match apologised to Liverpool supporters, had reported "significant and steady improvement" since the concussion and is expected to make a full recovery.