A key part of Boston's bullpen during the World Series championship season of 2013, Breslow struggled in '14, perhaps due to carryover fatigue from the year before.
The Red Sox traded lefty setup man Andrew Miller on July 31, and they then lost out on his services to the Yankees during free agency.
A nine-year veteran, Breslow has pitched in 479 Major League games, going 22-23 with a 3.20 ERA.
Breslow first pitched for the Red Sox in 2006, before moving on for stints with the Indians, Twins, D-backs and Athletics.
Boston reacquired Breslow in a trade with Arizona on July 31, 2012.
In 2013, Breslow sparkled for the Red Sox, posting a 1.91 ERA. Last season, he was largely ineffective for the first time in his career, notching a 5.96 ERA in 60 games.
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.