Casilla, who was replaced by Trevor Plouffe, is expected to get an MRI on his leg on Thursday, and the results will dictate whether the club will need to make a roster move.
"It's tough for Alexi," Twins manager Ron Gardenhire said. "We're going to have to wait and see what happens here with him. We're going to have an MRI on his leg. Whether it's a pull or a cramp, we don't know. First look at that didn't seem that bad."
Casilla said he's hopeful it's just a cramp, but said he knew something was wrong as soon as he started running out of the batter's box.
"I have no idea, but I felt like somebody put a knife in that spot," said Casilla, when asked if it was a strain or a cramp. "But I don't think it's that bad. Tomorrow we'll get an MRI and go from there, and see what the MRI shows. Maybe one or two days."