Stewart was placed on the 60-day disabled list Tuesday with a knee injury.
Stewart's knee began acting up again, so the Pirates opted to give him the rest of the season off. The veteran catcher will end the season with a meager .214 batting average as Pittsburgh's backup catcher, which likely won't help him garner a larger role moving into next season. Jacob Stallings was called up from Triple-A Indianapolis to take his spot on the roster.