Left-hander Drew Pomeranz made an emergency start in Kazmir's place against the Blue Jays in Thursday's 5-2 loss, allowing two runs in 1 2/3 innings on 44 pitches, and he's expected to remain in the rotation moving forward.
"He's been pretty versatile for us, whether it's in the bullpen or the rotation," A's manager Bob Melvin said. "It's always nice to have a lefty, and he's performed well in a starting role.
"It'll probably take a little while to where you can get six or seven innings out of him, but that's the plan with him."
Pomeranz has a 4.67 ERA in nine starts for the A's this year, compared to a 1.56 ERA in 20 appearances as a reliever, a role that seemed better suited for his repertoire.
Right-hander Chris Bassitt, meanwhile, is likely to assume Hahn's rotation spot come Saturday for the second of a three-game Interleague set in San Francisco. An official announcement is expected Friday.
Then there's Barry Zito, who could finally be nearing his chance at a return to the Majors in the second half. He's 6-7 with a 3.54 ERA in 20 starts for Triple-A Nashville this year.
"It makes it closer, gives him more of a shot now with Kaz going," Melvin said. "When it started out in Spring Training as a long shot, all he did was pitch himself into the potential of him coming here and this adds to that.
"We'll see where it goes from here with him, but he's certainly put himself in a position where anything could happen at any given time with him."
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, follow her on Twitter @JaneMLB and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.