"It didn't come out as favorably as I was hoping," Minnesota general manager Terry Ryan said. "We're going to have to shut him down for a while."
Ryan didn't put a specific timetable on when the club thinks Capps will be able to return, but said it would be longer than a 15-day DL stint.
Capps sustained the injury during an inning of work against Baltimore on Monday. It was just his second appearance after he missed 15 games on the DL with right shoulder inflammation.
The right-hander made two rehab appearances for Class A Advanced Fort Meyers before he was activated from the DL on July 13.
"There wasn't any urgency to rush back," Ryan said. "He was doing fine on the rehab assignment. [On Monday], he did something to irritate that thing."
Capps owns a 3.81 ERA in 29 appearances for Minnesota and has successfully converted 14 of 15 save opportunities.