Mujica has pitched in 13 games for the Red Sox, posting a 9.00 ERA. Opponents are hitting .340 against him.
Last week, the righty was slowed for a few days by tenderness in his right oblique.
"It's two outings, I think, in about a two-week span," said Red Sox manager John Farrell. "I temper it with ... he needs a little bit more frequent work. I don't necessarily see any restrictions physically after he felt something in the oblique. Still, he's a guy that's had a lot of success and we have to get him going."
Though Mujica was certainly in the running to be Boston's primary setup man, he was shaky out of the gate and Junichi Tazawa and Andrew Miller have been getting most of the high-leverage outs in front of closer Koji Uehara.
"I know he can be a little bit frustrated with the infrequency of use and the way things have gone to date," said Farrell. "We've got to get him a little more active and we've got to get him a little more consistent with overall location."
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.