The Arizona Diamondbacks activated staff ace Zac Gallen from the 15-day injured list Saturday for a home start against the Oakland Athletics.

The right-handed Gallen takes the roster spot of left-hander Brandon Hughes, who was optioned to Triple-A Reno late Friday.

Gallen has been sidelined since he injured his right hamstring against the New York Mets on May 30. He said he sustained the injury on his fifth pitch of the game and exited one pitch later.

Gallen (5-4, 3.12 ERA) placed third in National League Cy Young balloting last season after recording career highs for victories (17), strikeouts (220) and innings pitched (210). He also was the NL's starting pitcher in the All-Star Game.

Hughes, 28, had a 10.29 ERA in 12 appearances (two starts) this season, his first in Arizona after two seasons with the Chicago Cubs.