Bailey's stint on the DL will be postdated to April 29, the day after he last pitched, making him eligible to return on May 14.
The timing of his injury coincided with the return of Joel Hanrahan from the DL, which had led to questions regarding whether Bailey would retain the closer's job. Hanrahan had held the position at the beginning of the season.
Red Sox manager John Farrell decided to keep Bailey in the role, but the right-hander has not appeared in a game since Hanrahan came back. By default, Hanrahan has re-inherited his role.
Farrell said that an MRI confirmed the presence of inflammation in the muscle, but said the MRI showed no "structural changes or damage," which should give Bailey some "peace of mind."
"It confirmed the training staff's findings and what Andrew was feeling," Farrell said, "which should give him some peace of mind."
Hanrahan has pitched twice since returning from a strained right hamstring, giving up a run on two hits in a 9-7 loss to Toronto on April 30 and then registering a save with a scoreless inning in Toronto on Thursday, the last time he pitched.
"We're fortunate at this time to have a guy with his pedigree and success to close games out," Farrell said.
Bailey had a win, five saves and a 1.46 ERA in 13 appearances, striking out 20 in 12 1/3 innings.
Breslow missed all of spring training with inflammation in his left shoulder. He returns after making five appearances on rehab assignment, the first with Double-A Portland, the last four with Pawtucket. He pitched a scoreless inning against Durham in his last appearance Saturday.