The 32-year-old goalkeeper, who has long planned to leave the Nou Camp at the end of his contract in June, fell awkwardly while saving a free-kick from Fabian Orellana in the 22nd minute of the match, and could be seen crying as he left the pitch on a cart.
Barca confirmed the ACL tear after the match, a 3-0 win over Celta Vigo.
"Victor Valdes suffered an ACL tear on 22 minutes after saving a free-kick," the club said on their website. "The club's medical services confirm that he will need surgery."
Orellana's free-kick appeared to catch Valdes wrong-footed, and although he was able to make the stop he had to dive forward to gather the rebound, and it was then he suffered the injury.
He immediately called for help and was replaced by Sergio Pinto, who went on to make a fine double save in Barca's win.
The injury leaves an immediate question mark over Valdes' future as it will complicate any move to a new club this summer, while it will come as a blow to Vicente Del Bosque as he finalises his World Cup plans.