Doctors believe Liverpool goalkeeper Loris Karius was concussed as his side lost 3-1 to Real Madrid in the Champions League.
The 24-year-old German was at fault for the Spanish club’s first and third goals in Kiev on 26 May.
Karius had tests at hospitals in Boston in the United States, and medics said the impact of the concussion was "likely" to have been felt immediately.
The doctors have not pinpointed a time in the match at which he may have suffered the concussion but he collided with Real defender Sergio Ramos early in the second half.
Minutes after that collision, Karius threw the ball against Real striker Karim Benzema, and it rolled home to give the Spaniards the lead.
After being assessed at Massachusetts General Hospital and Spaulding Rehabilitation Hospital, he is said to have shown "significant and steady improvement since the concussive event".
Legal Show
Remix Saturdays
Bhangra Nights
Alim OnAir