Polanco suffered the injury when he slid awkwardly into second base in Friday's victory over the Miami Marlins. Polanco also suffered a significant bone bruise in his left knee on the play.
He was examined Wednesday by Dr. David Altchek at the Hospital for Special Surgery in New York. A timetable for his recovery has yet to be announced, though the team said his knee injury would require at least six weeks of rest.
The Pirates already had announced that Polanco, who batted .254 with a career-best 23 home runs and 81 RBIs in 130 games this season, would miss the remainder of the season.