Mujica was warming up in the bottom of the eighth inning to possibly relieve Jon Lester in the ninth with the Sox up at the time by a 6-0 score, but sat down after a few deliveries. Manager John Farrell called it "oblique tightness" for Mujica, who was taken by surprise by the sensation.
"I just felt a little pinch in there, and I've never felt that before," he said. "Something weird I felt."
Farrell talked before the game about Mujica's struggles. The manager said that Mujica is working on his delivery, trying to add more deception. Mujica, who has an ERA of 9.00 in 11 games, said that the tweaks in his windup had nothing to do with the injury.
Mujica received treatment Saturday and will check in with the trainers and staff when he arrives at the park Sunday before any decision is made on his status.