Liverpool goalkeeper Loris Karius suffered a concussion during his side's defeat to Real Madrid in the Champions League final.
The German was roundly criticised for his performance during the 3-1 loss in Kiev after two stunning 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.