Valdés went up to stop a free kick and landed with all his weight on his right knee. The goalkeeper was able to stand back up for a moment and them immediately went down in pain. There was little hesitation as a cart was brought out and Valdés was taken off the pitch with his hands covering his face.
At this point the exact nature of the injury is complete speculation, but based on the fact it was a non-contact injury and Valdés showing clear distress and frustration in the wake of going down will not give Barca fans many positives to cling to. If there's ligament damage, chances are Valdés season is done, along with his Barcelona career as he's leaving the club this summer when his contract expires.
Backup goalkeeper José Manuel Pinto entered the match in Valdés' place.