Sergio Aguero was forced out of the Camp Nou in the 41st minute after falling on his chest. The cause of the problem was not immediately clear.
He was treated for a few minutes and was taken off the bench, although the Argentine midfielder managed to get off the field.
“Sergio Aguero reported chest pains and was admitted to hospital for a heart test,” Barcelona confirmed in a statement after the Match.
Barcelona interim manager Sergi Barjuan said: “I asked him and he told me he was dizzy, I was told he had gone to the hospital, I don’t know anything else.
Memphis Depay opened the scoring for Barcelona in the 49th minute but Alaves equalized in the 52nd minute after Luis Rioja scored.
Barca sits 9th in La Liga point table.