(AP Photo/Nick Wass)

Nationals left fielder Bryce Harper underwent “successful” surgery to repair the ulnar collateral ligament in his left thumb, and the Nationals believe he will be sidelined between six and eight weeks, Manager Matt Williams said.

Harper posted a picture of himself on Twitter flashing a thumbs up (with his right hand, of course). Williams said Harper passed along a joking message saying he was already ready to start taking batting practice. Though Harper may be out until July, both he and the Nationals presented a cheerful front.

“It went fine,” Williams said. “We have to see how long that takes. The six-to-eight week time schedule is out there. We expect him to heal fast. He’s young. Given his history, he’s healed pretty fast. We’re optimistic about it, but unsure at this point how long exactly it will take.”

Harper, 21, started the season slowly but after the season’s first week has batted .345 with a .435 on-base percentage while slugging .534. He had just started find his swing, which he reworked as he returned from playing through a knee injury last year and offseason surgery.

With Harper out, the Nationals will turn primarily to Nate McLouth, with assistance from Kevin Frandsen, Tyler Moore and Steven Souza. The Nationals added McLouth expressly to prepare themselves for life without either Harper or Jayson Werth, but he will be hard pressed to make the same kind of impact Harper can.

“It hurts a lot,” Williams said. “He’s a fantastic player. We’ll certainly miss him. Guys have to step up and play well. At this point, he’s going to be out for an extended period. You just have to play and win our games.”

“You’re going to encounter some obstacles over the course of the season,” Werth said. “You don’t know what those obstacles are going to be. Going through the season, you know that you’re going to have to overcome some things. This is one of those things we’re going to have to overcome.”

Harper injured himself Friday, sliding into third base after a bases-loaded triple made the score 5-0 in the third inning against the Padres. It may seem tempting to fault Harper’s slide for injury. But he always slides headfirst, and he may have taken more of a risk had he used an unfamiliar technique and tried going in feet first. Headfirst slides are part of baseball and, unfortunately for the Nationals, so is bad luck.

“Guys are more comfortable one way or the other,” Williams said. “You look at Bryce, he had a collision at second base sliding feet first this year. He hurt himself last year sliding feet first. It’s something that you certainly can’t control. The play that he hurt himself on, he was trying to get to third base as quickly as he could. I don’t know if he’s safe if he slides feet first. Unfortunately, he got his thumb in the wrong position.”

Williams made clear he would not give orders on how the Nationals should slide.

“Certainly, we don’t want guys sliding into first,” Williams said. “But playing the game, you can’t legislate. You can’t say, ‘You have to do it this way.’ Because there are situations when the ball may be in your way, and you’re trying to get around a guy, and you have to slide headfirst. It’s unfortunate that he hurt his thumb. But they have to play the game the way they know how to play the game.”