In a corresponding move, the Rockies optioned right-handed reliever Chris Volstad to Colorado Springs.
Rockies manager Walt Weiss said the club wanted to bolster its left-handed bullpen depth because of a series of upcoming games against teams with batting lineups heavy with left-handed hitters.
"More than anything, it gives us another left-hander in the bullpen and Josh has been throwing well," Weiss said. "It gives us our best shot, especially here in the near future. Chris didn't perform poorly but he was in a situation where he wasn't getting a lot of consistent work. So, hopefully, he'll go down there and get that consistent work and I imagine he'll be with us again at some point this year."
Outman was 1-0 with a 0.84 ERA in five games for the Sky Sox. He had 14 strikeouts in 10 2/3 innings.
Volstad was 0-0 with an 8.53 ERA in four appearances for the Rockies covering 6 1/3 innings.