Washington Nationals left fielder Bryce Harper will undergo surgery Tuesday to repair a torn ulnar collateral ligament in his left thumb and is expected to be out until at least early July, according to multiple sources.

Harper, 21, injured his hand with a head-first slide into third base to cap a bases-clearing triple in Friday night's victory over San Diego. He stayed in the game for an inning before he was replaced.

The extended loss of Harper is a significant blow to a Nationals roster already riddled with injuries to key players, among them catcher Wilson Ramos, third baseman Ryan Zimmerman (both with hand injuries) and starting pitcher Doug Fister (back).

Harper missed 44 games last season, his second in the majors, with a left knee injury.