Nate McLouth. (Photo by Jonathan Newton / The Washington Post)

Nate McLouth will undergo season-ending shoulder surgery Thursday to repair a torn right labrum. The Nationals feared the veteran outfielder’s lingering shoulder injury was bad when it didn’t respond as well as expected to rest and treatment, and recent additional doctors’ evaluations and an x-ray with contrast dye revealed the tear.

McLouth has been playing with a hurt labrum all season, Manager Matt Williams said, but the symptoms got worse when he made a diving attempt for a triple in a July 28 game in Miami. “It hasn’t gotten any better since,” Williams said.

McLouth’s surgery means that veteran outfielder Nate Schierholtz, who inked a minor league deal with the Nationals on Monday, could be an option in the majors sooner than expected. Schierholtz reported to Class AAA Syracuse on Tuesday and is in the starting lineup.

The Nationals’ bench has lacked a left-handed hitter who can hit for power. Both Danny Espinosa and Jose Lobaton are switch hitters, but Lobaton is not usually a pinch-hitting option because he is the backup catcher. The rest of the current bench is right-handed: Kevin Frandsen, Scott Hairston and rookie Michael A. Taylor.

Should the Nationals decide to add Schierholtz as a left-handed hitter for the stretch run, he is a career .289 pinch hitter in the majors. The Nationals’ pinch hitters are worst in the National League with a .142 average and second to last with a .500 on-base-plus-slugging percentage.

Williams said McLouth is expected to be ready for 2015 spring training. When McLouth first landed on the disabled list on Aug. 4, the Nationals were hopeful the shoulder inflammation wouldn’t keep the outfielder out long. But McLouth had been playing with at least some discomfort for a while, the dive worsened it and the shoulder didn’t improve after rest.

“Everybody got a little bit of something in their throwing shoulder,” Williams said. “It was manageable, and he played all year last year and this year up to Miami. I think that dive really hurt him, and it just hasn’t been able to progress back to where he wanted it to be since that day. Decided to go ahead and get it fixed.”

McLouth has said the shoulder injury wasn’t the reason for his rough first season in Washington. The Nationals inked him to a two-year, $10.75 million contract hoping to shore up their bench, but McLouth hit .173/.280/.237 with one home run and 35 strikeouts in 79 games. But he did admit earlier this month that the balky shoulder hampered his preparation.

“No player will ever say and ever admit to something bothering you to [excuse a] lack of production,” Williams said Tuesday. “But you also look at last year. He played pretty regularly with no complications and no issues and did well. That’s something I don’t know. He never talked about it. We didn’t talk about that particular thing. But since he dove for that ball in Miami, that’s kind of the time frame when it started to get a lot worse.”

Williams said he isn’t concerned McLouth’s rehab from the surgery will prevent him being ready for spring training six months from now.

“The fact that he’s getting it done now gives him time to heal and rehab and get back,” Williams said. “Guys have it done in the offseason and they’re ready to go in spring training. It’s a little different for a pitcher, of course. But for a position player, especially an outfielder who doesn’t make as many throws as an infielder, it’s a little better rehab. He should be good.”