The three-time All-Star, who was already on the disabled list with a bruised right knee, had a 20-minute procedure in Philadelphia on Thursday to address a sports hernia.
The loss of Sizemore, who said the area had been bothering him since sliding into second base during a game in May, is a blow to an Indians team that is tied with Detroit for first place in the American League Central.
"Knowing the two areas are related and also learning my knee condition is not serious gives me peace of mind going forward that I can finish the season healthy and help contribute to an exciting pennant chase," Sizemore said in a statement.
The knee bruise ended a hot streak for Sizemore, who had hit .400 with two homers, two doubles and four runs batted in over six games.
For the season, he is batting .232 with 10 homers and 29 RBIs in 61 games.
(Reporting by Gene Cherry in Raleigh, North Carolina; Editing by Frank Pingue)