Thiago Alcantara has been ruled out of action for up to two months after rupturing ligaments in his right knee on Saturday.
The midfielder was a 75th minute substitute during Barcelona's 3-2 win over Sevilla - only to be injured late in the game.
A club statement read: "Tests performed on Sunday confirmed that the player suffered a rupture of the ligaments in his right knee.
"His absence is estimated at eight weeks."
Barcelona's next two matches are against Benfica in the Champions League and the El Clasico at home to Real Madrid.