Hahn's reaction was the same Tuesday as it was in July when he first received the news.
"The competitive side of me is a little bummed," he said.
The Padres have talked since the start of Spring Training about being vigilant regarding Hahn's innings. After throwing 69 innings last season, Hahn is at a combined 110 1/3 innings between stints with San Antonio and the Padres.
"My arms feels good, I don't feel tired ... I hope I'll be back here soon," Hahn said.
San Diego manager Bud Black said Hahn will return when the rosters expand -- from 25 to as many as 40 players -- on Sept. 1. What hasn't been determined, Black said, is if Hahn will return a starter or a reliever.
"I know this organization cares about me and cares about my arm," said Hahn, who missed the 2010 season after having Tommy John surgery and has been slowly been building his workload ever since.
Andrew Cashner will return from the disabled list this weekend and jump back into the starting rotation. He'll get a stat during a weekend series in Arizona, Black said.
To take Hahn's roster spot, the Padres promoted 24-year-old left-handed reliever Frank Garces from San Antonio. Garces had a 2.07 ERA in 61 innings with 44 hits allowed and 73 strikeouts.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.