WASHINGTON — When Bryce Harper couldn’t put any weight on his left leg when he was helped off the field, the worst-case scenario certainly seemed realistic.

Harper walking up the stairs provided some hope, and an MRI revealed what the Washington Nationals hope is season-saving news. General manager Mike Rizzo said Harper has a “significant” bone bruise in his left knee but avoided the kind of ligament or tendon damage that would have put a pin in the team’s World Series aspirations.

There’s no definitive timeline for Harper to return, but Rizzo is hopeful the star outfielder and NL MVP candidate will be back before the end of the season.

“Although we feel we’ve dodged a bullet a bit here with any long-term ligament and tendon damage, the bone bruise is something of significance, and we’re going to treat him cautiously and hopefully have him back later on this season,” Rizzo said Sunday morning. “We put ourselves in a position that we can treat it cautiously and we’ll continue down that road.”

Harper injured his knee when he slipped on a wet first base in the first inning of a rain-delayed game against the San Francisco Giants on Saturday night. Rizzo said the conditions, which included steady rain during the play “aided” in the injury but didn’t blame Major League Baseball for going ahead with the game.

“It was something that happened,” Rizzo said. “That’s baseball. We have to roll with that.”

Harper is expected to speak to reporters on Sunday afternoon. The 2015 MVP is hitting .326 with 29 home runs and 87 RBIs in 106 games this season, and his presence in the lineup is crucial to Washington playing deep into October.

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The Nationals running away with the NL East gives them the luxury of playing it safe with Harper. Given injuries to Harper, Stephen Strasburg — who has a rehab assignment Monday — and others, the Nationals’ focus is getting healthy for the playoffs.

That’s especially important considering Harper can be a free agent after the 2018 season, crystallizing Washington’s championship window with Max Scherzer in his prime and a lineup built with power around the 29-year-old face of the franchise, Daniel Murphy, Trea Turner, Anthony Rendon and Ryan Zimmerman. Even injuries to Strasburg, Turner, Jayson Werth and more haven’t hurt the Nationals yet because of their organizational depth.

“When talking about building an organization, you’d be short-sighted you’d be short-sighted to think about the 25 men on the major league roster,” Rizzo said. “This is a 40-, 50-man operation and you have to rely on great scouting to bring the players and great development to get these guys ready to play at an optimal level in a pennant race for the Washington Nationals, which is not easy.”

The injury to Harper opens up playing time in the outfield but would present a difficult challenge if he’s not ready by the start of the postseason. The Nationals don’t have another Harper in the system, and neither does anyone else in baseball.

“He’s definitely one of those guys that you can’t replace on a team,” starter Edwin Jackson said.