Walters gave up four straight singles and two runs to begin the game against the Philadelphia Phillies on Wednesday night, before manager Ron Gardenhire came out to the mound.
Gardenhire appeared to give the glum-faced Walters a lecture, then assistant athletic trainer Dave Pruemer joined the group. Seconds later, the call was made to the bullpen for right-hander Jeff Manship.
The Twins announced later that Walters could not get loose. He'll have an MRI exam on Thursday.
Walters, making his seventh start since being called up from Triple-A Rochester, saw his ERA soar from 4.42 to 5.40.