Barcelona captain Andres Iniesta was taken off on a stretcher following a heavy challenge from Enzo Perez in the first half of Saturday's match with Valencia.
The Spain international appeared to jar his right leg as Perez slid in with a robust tackle after 14 minutes at Mestalla.
Iniesta immediately signalled to the bench as he clutched at his lower knee, and he was carried off on a stretcher after being treated by medical staff on the pitch, with Ivan Rakitic replacing him.
The home fans joined the Barca faithful in applauding Iniesta from the pitch, with a number chanting his name as he was taken down the tunnel.
Head coach Luis Enrique was furious at the challenge that left the 31-year-old in obvious pain, with Perez - who did play the ball - escaping a yellow card.
Barca have been blighted by injuries this week, with Jordi Alba and Gerard Pique both forced off in the Champions League win over Manchester City, while Arda Turan and Rafinha picked up knocks in training that ruled them out of Saturday's game.