The Pirates announced Saturday that Polanco has a significant bone bruise in his left knee, an injury that requires at least six weeks of rest. The team will seek a second opinion before determining a treatment plan for Polanco.
Polanco suffered the injury when he slid awkwardly into second base in Friday's victory over the Miami Marlins. The Pirates said Polanco also injured his shoulder on the play.
Polanco, 26, batted .254 with a career-best 23 home runs and 81 RBIs in 130 games this season, his fifth with the Pirates.