Price was placed on the DL on July 28 due to inflammation in his pitching elbow.
The southpaw also began the season on the DL with an elbow ailment, and he has made just 11 starts this season.
Price owns a 5-3 record to go along with a 3.82 ERA, 1.27 WHIP and 63 strikeouts in 66 innings.
The 32-year-old veteran is a five-time All-Star and former Cy Young award winner as a starter, but due to Boston's depth in its rotation, it is planning to use him out of the bullpen.
Provided Boston's rotation—featuring Chris Sale, Drew Pomeranz, Rick Porcello, Eduardo Rodriguez and Doug Fister—remains healthy and effective, Price could be a huge weapon down the stretch and in the playoffs.
Pitching out of the pen isn't foreign to Price, as he served in that role for the Tampa Bay Rays during their run to the World Series in the 2008 postseason.
Price has traditionally struggled in the playoffs as a starter, but in adding him to a pen that already includes Craig Kimbrel and Addison Reed, the Red Sox will be a tough team to beat in October when they get a lead.