Bryce Harper will undergo surgery to stabilize his broken left thumb, sources told ESPN, confirming multiple reports.

The Philadelphia Phillies outfielder was injured after being hit by a 97 mph fastball from Blake Snell in the fourth inning of Saturday night's win against the San Diego Padres.

The Phillies announced Sunday that Harper will be out indefinitely with the injury and put him on the 10-day injured list.

Harper, the reigning National League MVP, is hitting .318 with 15 home runs, 48 RBIs and a .985 OPS this season in 64 games despite a small tear in the UCL of his right elbow that has prevented him from playing the outfield since April 16. He has tried to avoid season-ending Tommy John surgery with a platelet-rich plasma injection and rest.

Information from The Associated Press was used in this report.