Karius collided with Sergio Ramos during a Real Madrid corner early in the second half, and moments later he was at fault for Karim Benzema’s goal.
The 24-year-old also erred for Madrid’s third goal, failing to deal with Gareth Bale’s long-range shot as the Spaniards ran out 3-1 winners.
Liverpool’s medical staff were worried Karius may have suffered concussion and arranged a scan while he holidayed in the US.
Liverpool declined to comment when contacted.
Karius, who missed out on a place in Germany’s World Cup squad, apologised to Liverpool supporters for his gaffes.
“I know that I messed it up with the two mistakes and let you all down,” he said. “As I said I’d just like to turn back the time but that’s not possible. It’s even worse as we all felt that we could have beaten Real Madrid and we were in the game for a long time.”