The striker did not feature in the team's 2-1 win at Crystal Palace on Saturday due to the hamstring problem that has dogged him in recent weeks.
However, Mourinho refused to reveal whether the Spanish international would be sidelined for Sunday's trip to Manchester United.
"Tomorrow he can't play. He can't do it tomorrow," the Portuguese told reporters at a press conference. "It's the same problem that he's been having. He cannot play tomorrow but I don't have any idea how long he will be out for."