Los Angeles Angels star outfielder Mike Trout has a torn meniscus in his left knee and will undergo surgery that will keep him out for an undetermined amount of time.

Trout, who is expected to return at some point this season, was off to a hot start with 10 home runs to tie for the most in the major leagues heading into today’s play. He also had 14 RBIs and an .867 OPS in 29 games.

Trout was formally moved to the 10-day injured list tonight. In turn, the Angels signed free agent outfielder Kevin Pillar to a one-year, $740,000 contract.

Recent injuries have prevented Trout from playing in 100 games for three of the previous four seasons. The 32-year-old was limited to 82 games last season after he fractured the hamate bone in his left hand.

A three-time MVP, Trout is a career .299 hitter but was batting just .220 this season. He has 378 career home runs with 954 RBIs over 1,518 games over 14 seasons, all with the Angels after he was a first-round draft pick (25th overall) in 2009.

The American League Rookie of the Year in 2012 is an 11-time All-Star.

Pillar, 35, designated for assignment by the Chicago White Sox on Friday and elected free agency. He batted .160 (4-for-25) in 17 games for the White Sox this season but is a career .257 batter with 107 homers and 427 RBIs for eight teams across 12 seasons.

In other roster moves, the Angels also selected the contract of left-hander Amir Garrett, optioned right-hander Davis Daniel to Triple-A Salt Lake and transferred infielder Michael Stefanic and right-hander Chase Silseth to the 60-day IL.