Ziegler's stint is retroactive to Wednesday. The submarine-style-throwing right-hander said he has dealt with discomfort since March, and he had an MRI exam taken on his back Wednesday. He was awaiting the results Thursday.
"I first felt it back in March," Ziegler said. "I was trying to gut through it. There were times it'd feel better than others. It wouldn't go away. As my usage increased, there would be times I'd be spending two hours in the training room trying just to get ready for the game that night."
Tazawa went on the DL on May 17 with right rib cartilage inflammation, and on Tuesday he was sent on rehab assignment to Triple-A New Orleans.
Ziegler has a 6.52 ERA in 34 games, posting a WHIP of 1.83 in his 29 innings. In Ziegler's most recent outing on Tuesday against the Nationals, he allowed five runs (three earned) on four hits in one inning.
Ziegler had a strong April, posting a 0.71 ERA, but he has struggled with an ERA of 6.14 in June.
Tazawa entered play Thursday with a 6.60 ERA in 15 innings this season, allowing four home runs in his 16 appearances.
"There's no problem with my recovery," Tazawa said through his interpreter. "I just want to contribute to help the team."