PHILADELPHIA -- Bryce Harper could not continue Sunday at Citizens Bank Park. His ability to play the final week of the Phillies’ season could determine their postseason fate with only seven games to play.

Harper left the 6-3 loss to the Blue Jays in the seventh inning because of stiffness in his lower back.

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Is it serious? Is it just a tweak?

Only Harper can say, and he was not available for comment. But he looked uncomfortable throughout the seventh inning. He bent at the waist for a moment in right field after chasing down a triple in the top of the inning. Harper then grabbed the left side of his hip after fouling off a 2-2 fastball in the bottom of the inning. He struck out swinging.

Once he returned to the dugout, he got the attention of Phillies bench coach Rob Thomson. He made a gesture across his throat, signaling he was done for the day, and he pointed to the left side of his back.

Phillies manager Joe Girardi turned to Thomson. His eyes widened.

His eyes seemed to say, “Wait, what? Not Bryce, too.”

Yes, Bryce, too.

If Harper is unable to play, even just a game or two this week, it would be a major blow to the Phillies’ postseason chances. Philadelphia is already without J.T. Realmuto and Rhys Hoskins. Neither has played since Sept. 12.

Realmuto’s strained left hip flexor is feeling better, but Girardi said he will not catch in Monday night’s series opener against the Nationals in Washington. There is an outside chance he could serve as the club's designated hitter. Hoskins has a strained ulnar collateral ligament in his left arm. He is further away than Realmuto, though he hopes to pick up a bat in the next couple days just to see if he can hit before next Sunday’s series finale in St. Petersburg against the Rays.

Losing three of the top four hitters in the lineup could be impossible to overcome, especially because Harper has been swinging the bat well lately. He is hitting .277 with five doubles, four home runs, seven RBIs and a 1.009 OPS in his last 13 games.

The Phils have little margin for error at this point. Sunday’s loss dropped the team to 27-26. While they still hold the seventh seed in the eight-team National League postseason field, the Giants, Reds and Brewers -- all tied for the No. 8 seed -- each won Sunday to move to within a half-game of Philadelphia.

Harper received treatment after the game. Girardi indicated that his star outfielder could receive more treatment at the team’s hotel outside Washington on Sunday night, and again Monday morning.

“We’ll see how he feels tomorrow,” Girardi said on Sunday evening. “We’ll see if he’s available for me tomorrow. He’ll get a lot of treatment and [we'll] keep our fingers crossed.”

Harper has battled back issues throughout the season, although it had not visibly popped up until Sunday.

“Nothing that has limited him, in a sense, to where we couldn’t play him,” Girardi said. “But I think he’s dealt with it from time to time, yeah. Once you have a back issue, it seems like you never, ever get rid of it completely. It finds a way to rear its ugly head.”

Phillies rookie Adonis Medina allowed two runs in four innings in his MLB debut, but the defense helped the Blue Jays score their first four runs. First baseman Alec Bohm touched a ball in fair territory that could have been foul, which led to Toronto's two runs in the first inning. Left fielder Adam Haseley got a bad jump and could not get to a fly ball in the sixth, which turned into a two-out, two-run double. The ball had a 70-percent catch probability, according to Statcast.

Right-hander Heath Hembree then allowed a two-run homer in the seventh to make it 6-1. Hembree has a 12.54 ERA (13 earned runs in 9 1/3 innings) in 11 appearances since joining the Phillies on Aug. 21. He has allowed 17 hits, including two doubles, one triple and seven home runs.

But Harper overshadowed it all. They need him back. Will they get him back?

They hope to know Monday.