Washington Nationals left fielder Bryce Harper will undergo surgery Tuesday to repair a torn ulnar collateral ligament in his left thumb and could be out until at least early July, ESPN.com reported Monday.
Harper, 21, suffered the injury during a head-first slide into third on a bases-clearing triple in Friday's victory over San Diego. He stayed in the game for an inning before being replaced.
The Nationals placed Harper on the disabled list Sunday and backdated the move to Saturday.
Harper was scheduled to see a hand specialist Monday to get more information about the injury's extent.
Los Angeles Angels outfielder Josh Hamilton injured a thumb in similar fashion to Harper by sliding head-first into a base and is out six to eight weeks.
Nationals manager Matt Williams said after the game that X-rays were negative. Harper missed Saturday's game. He was replaced in left field over the weekend by Kevin Frandsen but Nate McLouth may take over.
Harper is batting .289 this year but has just one home run in 83 at-bats. He was limited to 118 games in 2013 because of hip, knee and side injuries.
Williams said Harper did nothing wrong in the way he slid into the base.
"It's happens all the time," Williams said. "Guys slide in headfirst all the time. Just so happens that he got his thumb in an awkward position. You can't question that. You can't question the way the kid plays the game. He plays the game hard."