WASHINGTON -- When Bryce Harper writhed in pain on the field and clutched at his left knee and then didn't put weight on his left leg as he was helped off, the possibility of a career-altering injury seemed realistic.

Harper was definitely worried.

"Of course you're going to think the worst,'' he said. "It's definitely a bad feeling.''

That bad feeling subsided as Harper walked up the stairs from the dugout to the clubhouse, tested his knee by jumping up and down and then got the MRI results that 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 manager Dusty Baker referenced 10 days to two weeks. At the very least the Nationals are hopeful the star outfielder and NL MVP candidate will be back before the end of the season.

"It was definitely a relief,'' Harper said Sunday. "We're going to take some time to definitely let it heal. I want to be at 100 percent whenever I play. The World Series is definitely on my mind, playoffs, things like that.''

Rizzo said the Nationals feel they "dodged a bullet'' but didn't want to undersell the significance of the bone bruise, which came when Harper hyperextended his knee slipping on a wet base in the first inning of a rain-delayed game against the San Francisco Giants on Saturday night.

"The bone bruise, it's real,'' Rizzo said. "It's an injury, and we're going to have to treat it accordingly.''

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. Harper was upset about playing in the rain at 10 p.m. but called it a "freak accident.''

"I don't like wet bases,'' Harper said. "It's just an unfortunate situation that happened. There's nothing I can do.''

Harper, 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.

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.

"We don't know how long he's going to be out, but he will be back before the end of the season,'' Baker said. "We expect him to be back for the stretch drive and be healthy. That's what we want.''

This fall is 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.

Harper knows that and vowed not to play through an injury -- unless it's the playoffs. At that point, all bets are off.

"If I don't feel good, then I'm not going to go out there and play,'' Harper said. "Of course if we were in the playoffs right now I'd tape it up and get out there and hobble the best I could and do that.''