Harper was removed from Thursday's contest due to groin tightness, Dan Kolko of MASN reports.
The young superstar was lifted from the game in the seventh inning in favor of Chris Heisey, and although it wasn't revealed at the time, the Nationals seemed to just be playing things safely with Harper while they held the lead. Consider Harper day-to-day for now, with more details on his availability moving forward likely coming as Friday's start time approaches.