Iniesta was stretchered from the field in tears after just 14 minutes, but fears he could be sidelined for months were eased by tests upon his return to Barcelona.
"After the first diagnosis carried out at Mestalla, the tests in Barcelona have shown the extent of the injury," Barca said in a statement.
"The timeout is between six and eight weeks." Iniesta could now return in time to face Real Madrid in the first El Clasico of the season on December 3.
However, he will miss Barca's Champions League trips to Manchester City and Celtic next month. Barca had earlier confirmed Iniesta had injured the lateral collateral ligament in his right knee.
Coach Luis Enrique was incensed when Valencia's Argentine midfielder Enzo Perez escaped without even a yellow card for the challenge that caused the injury.
"We saw very clearly from the tackle it was an injury and a serious one," said Enrique. "We will see tomorrow, but it will be weeks. There wasn't even a yellow card."
Barca's season has been plagued by injuries so far as Lionel Messi has just returned from nearly a month out, whilst Gerard Pique and Jordi Alba were injured in Wednesday's 4-0 win over Manchester City.
Messi has returned in fine form, though, as his sixth goal in three games since his comeback deep into stoppage time from the penalty spot moved Barca to the top of La Liga.