Barrett had a 3.86 ERA in six games for the D-backs before his demotion, and he threw 2 2/3 scoreless innings in Reno.
With the D-backs' starting rotation not pitching deep into games and three extra-inning games so far this season entering Thursday's series finale vs. the Cardinals, the bullpen has been taxed. That has necessitated a flurry of moves involving young pitchers who still have Minor League options.
That was why Barrett was not surprised by his demotion.
"I wouldn't say expected, but when you're coming off an extra-inning game and you're one of a couple guys that have options on the team, you have a feeling it's going to happen," he said.
In other D-backs news, injured right-hander Josh Collmenter threw two innings in an extended spring game and allowed three runs on four hits while striking out four. He faced nine batters and threw 28 pitches.
Collmenter is scheduled to throw next for Class A Advanced Visalia.
Steve Gilbert has covered the D-backs for MLB.com since 2001. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.