The Baltimore Orioles placed starter Jason Hammel on the 15-day disabled list Sunday with a right knee injury.
Hammel will undergo arthroscopic surgery and is expected to be sidelined at least 3-to-4 weeks.
He left Friday night's loss to Detroit after injuring his right knee throwing to the first batter in the fourth inning.
The 29-year-old took some warmup throws to see if he could remain in the game but was lifted instead for Luis Ayala.
Acquired in the offseason -- along with reliever Matt Lindstrom -- from the Colorado Rockies in exchange for pitcher Jeremy Guthrie, Hammel is 8-6 with a 3.54 ERA in 18 games started this season. He leads all Baltimore pitchers with 106 strikeouts.
To fill Hammel's spot on the roster, Baltimore recalled pitcher Steve Johnson from Triple-A Norfolk.