"We'll give him some therapy for the next four or five days," Twins general manager Terry Ryan said Thursday. "He came in this morning a little sore. He didn't know exactly what it was."
The Twins described the injury as a precursor to a stress fracture. An MRI found nothing more serious.
"He should be OK after a little treatment," Ryan said. "That would be the hope. I think we're OK."
Mauer, last season's American League batting champion, hurt his left knee in his rookie season in 2004.
Mauer was to be treated with a bone stimulator and physical therapy and was to be re-evaluated Sunday, Twins spokesman Mike Herman said.
"Basically all that we know right now is they caught it early, obviously before it turned into a stress fracture," Herman said. "They're shutting him down until Sunday."
Mauer, a St. Paul native, was the first player taken in the 2001 draft. He missed most of his rookie year after tearing the meniscus in his left knee but bounced back to hit .294 in 2005 and then hit .347 last season.
Mauer, 23, agreed to a $33 million, four-year contract in the offseason to avoid arbitration.