Atletico Madrid striker Fernando Torres was taken to hospital after suffering a head injury in Thursday's 1-1 draw with Deportivo La Coruna.
Torres collided with Depor substitute Alex Bergantinos as they both went to head the ball in the 85th minute of the league contest at the Riazor.
The former Liverpool and Chelsea frontman then crashed heavily to the turf, with his head clattering against the ground.
With players from both sides appearing very concerned by what they had seen, medical staff rushed over and Torres, who at least initially seemed to be unconscious, was subsequently taken off the pitch on a stretcher.
Atletico later released a statement that said: "Torres suffered a head trauma. He was taken to hospital for tests. He will spend the night under observation."
Diego Simeone's side had fallen behind in the 13th minute when Florin Andone slotted in, before Antoine Griezmann equalised with a spectacular 68th-minute strike.