Iniesta, who scored the goal at Chelsea that put Barca in last season's Champions League final and is a key member of Vicente del Bosque's Spain squad, will be out for about a month, Barca said on their website.
He is certain to miss the clash against Inter, with the first leg in Milan on April 20 and the return on April 28, but could be back for the trip to Sevilla on the weekend of May 8/9 - Barca's penultimate game of the La Liga season.
The Champions League final is on May 22 in Madrid and the 2010 World Cup in South Africa starts in June.
"It is one of the most difficult moments I've had to go through," Iniesta said on his Twitter feed.
"Life has taught me never to give up."
The 25-year-old has struggled with a string of thigh problems over the last year.
He played last year's Champions League final carrying a thigh injury and was forced to drop out of Spain's trip to South Africa to compete in the Confederations Cup when it was diagnosed as more serious than had first been thought.
He has had trouble with thigh injuries in both legs this season, and was unable to take part in the World Club Cup final last December.
As a result the midfielder has failed to hit the form that made him one of Barcelona's outstanding players in their treble-winning campaign.
It will be worrying news for Spain boss Del Bosque as he fine tunes his plans for South Africa.
