Coulombe was optioned to Triple-A Nashville on Wednesday.
The lefty reliever had a rocky first outing with the A's, but he settled down over his next two appearances, throwing 3.2 scoreless innings with three strikeouts and no walks. However, with Jed Lowrie and Zach Neal coming back to the big league club Wednesday, Coulombe's spot on the roster was in jeopardy to begin with. He'll head back to Triple-A Nashville, where he figures to continue to work out of the bullpen.