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 sources.

The 21-year-old injured his hand during a head-first slide into third on a bases-clearing triple in Friday's game against the San Diego Padres.

"I slid into the bag and I caught it a little bit," Harper said. "Went into the dugout, swung a couple in the cage, felt fine. Went out to the outfield, it swelled up a little bit. ... So I got in and got some treatment on it."

Harper is hitting .289/.352/.422 with one home run and 9 RBIs.