Harper was removed from Tuesday's game against the Dodgers with lower-back tightness, Matt Breen of The Philadelphia Inquirer reports.
The 28-year-old had the injury crop up on a swing during his fourth-inning strikeout, and he didn't take the field for the bottom of the frame. Harper dealt with the same injury in mid-April and only missed one game, though the severity of the issue this time around remains unclear.