The shot-stopper was stretchered off against Celta on Wednesday and will not play for the Catalans again or be fit for the World Cup.
The Spain goalkeeper picked up the injury with little over after 20 minutes played, after diving on a loose ball in the box having failed to clear a free kick from Fabian Orellana.
He immediately went to ground, clutching his right knee and called for medical aid. After a couple of minutes of treatment on the field, he was taken off the park covering his face, with Jose Pinto replacing him.
Barcelona said in a statement after the match: "Valdes has torn the anterior cruciate ligament in his right knee and will require surgery."
The 32-year-old has already announced that he will leave Barca when his contract expires in June and his injury means he will not feature again for the Catalans.
In addition, the shot-stopper's injury has eradicated his chances of playing in the World Cup for Spain this summer.