The Spain international had to be removed from the pitch on a stretcher after sustaining damage to the lateral collateral ligament of his right knee in a heavy challenge from Enzo Perez in the first half of Saturday’s 3-2 victory over Valencia.
Barca earlier confirmed Iniesta had sustained ligament damage and would undergo further tests to find out the full extent of the injury upon his return to Catalonia.
The midfielder has now been ruled out of action for up to two months.
An official club statement read: “Andres Iniesta has a partial injury to the lateral collateral ligament in his right knee. Time out of action is approximately six to eight weeks.”
Iniesta is now a major doubt for the Clasico against Real Madrid at Camp Nou on December 4, which is almost exactly six weeks away.
It is another blow for Luis Enrique, who lost key defensive duo Jordi Alba and Gerard Pique to short-term injuries in the 4-0 victory over Manchester City.