Oakland made the roster move on Monday as expected.
Ross made a spot start for the A's in St. Petersburg on Aug. 24, and like his previous stints this season, he struggled. He was immediately sent back down to Triple-A Sacramento following the outing to begin work as a reliever, having posted a 6.45 ERA in 13 games as a starter.
"We really feel like, with this stuff, he can just try to rely on two pitches out of the bullpen and not pace himself but just go out there and go as hard as he can for however long as he's out there," manager Bob Melvin said. "I think you see the velocity pick up some, too. He's got the ability to get ground balls, and all those variables, we think, can make him a good reliever."
With Ross aboard, the A's have nine relievers in their bullpen.