Harper exited Sunday’s 6-3 loss to the Toronto Blue after he struck out with the bases loaded in the seventh inning. The Phillies right fielder took a slow walk in the dugout toward the clubhouse and signaled to manager Joe Girardi he was done for the day.

Harper was hitting second in the lineup Monday for the start of a four-game series with the Nationals, his former team.

Girardi said he could also use Harper as the DH in one of the two games of Tuesday’s doubleheader.

“Hopefully this will kind of refresh him,” Girardi said before Monday’s game. “We’re just in a brutal part of the schedule and he just had some back tightness.”

The Phillies are currently the seventh seed in the NL playoff race. Harper, in the second year of a $330 million, 13-year deal, has 11 home runs and 28 RBIs and is batting .260 in 51 games this season. He leads the league with 41 walks.

Phillies catcher J.T. Realmuto was out of the lineup again with a strained left hip flexor. Realmuto missed the last 10 games but could be available to pinch hit Monday night.