Mauer was placed on the 15-day disabled list Thursday after complaining of weakness in his upper legs and soreness in his hips and other parts of his body.
The all-star backstop was hospitalized with flu-like symptoms and tests returned Friday indicated he is suffering from an infection, Manager Ron Gardenhire told the (Minneapolis) Star Tribune.
"Basically, that really kind of helps us through this whole process of the leg stuff and all that," Gardenhire said. "It tells us that there's probably a reason why he's been so sore, and that's his system is fighting a viral infection.
"It kind of helps us in knowing a little bit better in where we stand and what's really going on."
Twins General Manager Bill Smith told KSTP-AM, St. Paul, he was confident Mauer's condition is not a long-term problem.
The Star Tribune reported Mauer Friday was recuperating at the team's hotel and would accompany the squad to Baltimore Sunday, where he will consult with a Johns Hopkins Hospital physician.