(Katherine Frey/The Washington Post)

As the Washington Nationals’ season creeps closer to the precipice, 20-year-old outfielder Bryce Harper will visit renowned orthopedic surgeon  James Andrews on Monday to receive another opinion on his swollen left knee, which has seen little improvement even though Harper hasn’t played since May 26.

Harper, the Nationals’ best, most dynamic player in his second season, first injured his knee May 13 in Los Angeles, when he crashed into the right field wall at Dodger Stadium. He toggled in and out of the lineup for more than two weeks before continued wear on his knee brought him too much pain to continue. He aggravated the injury with two head-first slides and a foul ball off his left knee on May 26 against the Philadelphia Phillies in Washington.

“If [the swelling is] still there and not getting better I’m not going to rush it and take as much time as I can to get right,” Harper said before Thursday’s game. “I want to get back in this lineup 100 percent. I don’t want to get back in it 80 percent. Just trying to get it better as much as I can.”

The Nationals, depleted by injuries in a season that began with playoff expectations, continued to call Harper’s injury a “day-to-day” ordeal until Saturday, when they placed him on the disabled list with left knee bursitis. Even the day after Harper crashed into the wall in Los Angeles, General Manager Mike Rizzo said Harper was considered “day-to-day.” On Sunday, Harper admitted he probably should have gone on the disabled list on April 30 after he banged his left side into the right field fence in Atlanta while trying to rob a home run.

Manager Davey Johnson had few guesses about what the Nationals could expect from Harper’s visit with Andrews, the surgeon who operated on Redskins quarterback Robert Griffin III’s knee last winter. Harper will leave the Nationals on Sunday night and visit Andrews early Monday morning.

“Everybody says it’s bursitis,” Johnson said. “I thought normally you usually take anti-inflammatory and kind of calm it down. But it’s kind of been lingering. When he runs, it swells up. He did some light jogging in the pool, and it swelled up. We’re concerned.”

Harper tested his knee by running and hitting in Baltimore on May 30, three days following the aggravation. He couldn’t run at full speed, and Johnson caught him limping afterward and the following day when he walked off the team plane in Atlanta. The Nationals have said that Harper’s knee injury isn’t structural and once the swelling lessened he could return to the field.

Johnson said there wasn’t enough fluid in the bursa sac to be drained. Surgery to remove the troublesome sac is typically the last resort, Johnson said, and if Harper underwent that procedure he would be out at least another two to three weeks.

Harper said Thursday he had felt little improvement despite his rest. He tried jogging with his lower underwater in a pool Thursday, but had to stop when pain surfaced. The swelling “hasn’t really gone down at all,” Harper said.

After his first crash into the wall in Atlanta, Harper continued to play and his condition worsened when he slammed violently into the right field wall in Los Angeles two weeks later. Two days after receiving stitches on his chin and tests for a concussion, Harper pinch hit and started the next day, May 16. He played two full games before his balky knee forced him to sit. He returned again on May 20 after missing two games. He started six games before aggravating the injury sliding into second base May 26. Harper has sat three times while recovering from the lingering effects of the same wall collision in Los Angeles.

The Nationals offense was already struggling with Harper’s bat in it. Since the injury, it has worsened. The Nationals are 25-18 with Harper in the lineup and 4-12 when he doesn’t start. Even though he hasn’t played in nearly two weeks, and little over the past month, Harper leads the Nationals in several offensive categories. But after his first encounter with a wall in Atlanta, it was clear his health and performance had been affected. Before Harper slammed into the wall in Atlanta, he was hitting .360/.444/.756. Since then, Harper has hit .188/.312/.359.

Harper is on a growing list of key Nationals to miss time due to injury. A preseason World Series favorite, the Nationals have seven players on their 40-man roster on the disabled list. Two-fifths of the starting rotation — Stephen Strasburg (lat) and Ross Detwiler (oblique) – are injured. Danny Espinosa (wrist), Ryan Mattheus (hand), Wilson Ramos (hamstring) and Christian Garcia (forearm) are also on the disabled list. Including Thursday’s game, the Nationals players have missed a combined 203 games to the DL.

“We’re getting healthier as far as I’m concerned,” Johnson said. “It’s a long season. We’ve gone through some injuries. I think we’re going to come out of it alright. We got the guys here to do it. We need to get on with it.”