He could be activated soon, perhaps by Monday, when the Sox open a homestand against the Twins.
"He's certainly getting closer," said Red Sox manager John Farrell. "Certainly we'll review that internally and determine if that's going to be when we return immediately on the homestand, or is there an additional need for another appearance? Still, the most important thing is, with each outing, he's gotten more crisp with all his pitches and moving in the right direction."
With Franklin Morales also sidelined, Andrew Miller has been Boston's lone lefty in the bullpen.
The return of Breslow could give Farrell a significant advantage with in-game strategy.
"Well, it gives you the ability to match up if you need to earlier in the game," Farrell said. "Craig is a proven mid- to late-inning reliever. So any time you can add that experience and that performance level, that's going to be a good thing. However, we can't look past what Alex Wilson did for us last night, giving us the nearly three innings of work. So Craig's return to us, as we mentioned with Joel's healthy return, will continue to give us a boost."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.