Second baseman Jean Segura, fifth in the majors with a .332 batting average, also exited with an apparent left groin injury after beating out a grounder with two outs in the ninth. Philadelphia manager Joe Girardi said Harper is day to day, but he's concerned Segura will be out longer.
Harper struck out swinging to end the top of the fourth. He was 0-for-2 on the night at Dodger Stadium as the Phillies lost 5-3.
In the bottom of the fourth, Luke Williams shifted from shortstop to right field and Ronald Torreyes took Harper's spot in the lineup, batting fourth at shortstop.
Harper exits with back tightness after striking out
Bryce Harper strikes out in the fourth inning then leaves the Phillies' loss to the Dodgers with a back issue.