O'Hearn (quadriceps) will begin a rehab assignment with Triple-A Indianapolis on Tuesday, Colin Beazley of the Pittsburgh Post-Gazette reports.
O'Hearn has not played in a game since he went down with a left quad strain in late July, but he's been cleared to test things out at the Pirates' top minor-league affiliate. The 31-year-old is aiming to be reinstated to the active roster ahead of this weekend's series at Wrigley Field against the Cubs.