Bart was removed from Tuesday's game against the Diamondbacks after being hit in the head with a backswing, Noah Hiles of the Pittsburgh Post-Gazette reports.
Interim manager Don Kelly said after the game that Bart is still being evaluated, so it's unclear if he's suffered a concussion. Regardless, the 28-year-old seems likely to sit out Wednesday afternoon's series finale in Arizona after starting the first two games of the series.