The catcher was taken to a St. Petersburg hospital with flu-like symptoms following Thursday night's 4-3 loss to the Rays, and it was discovered that a viral infection is likely the cause of what was labeled "bilateral leg weakness" on Thursday.
Instead of complications from offseason surgery the four-time All-Star had on his left knee, or something even worse, Mauer's soreness this week can be blamed on the flu bug. And that, manager Ron Gardenhire said, is very good news.
"That really kind of helps us through this whole process of the leg stuff," Gardenhire said. "It tells us that there's probably a reason why he's been so sore, and that's [because] 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."
Mauer's recent struggles were a surprise to those behind the scenes during Spring Training this year. Gardenhire told tales of the 27-year-old reporting at 6 a.m. daily for his exercises, and of the strength he gained throughout the exhibition season.
"We were very cautious, and got him all the way through mid-Spring Training," Gardenhire said. "Once Joe felt that his legs were good enough to get back behind the plate and start catching, he started doing that, and by the end of Spring Training, he felt wonderful. He felt great.
"By the time we got to Baltimore for our exhibition games, he was feeling as good as he's ever felt. He was swinging good in Spring Training, and it continued. He was going along pretty good. I checked with him every day."
Mauer then played nine regular-season games and hit .235 (8-for-34). He expressed concern about soreness after the April 7 game in New York but went on to play four consecutive games before taking a break on Wednesday. The malady intensified during that time, leading him to approach the Twins' staff and, eventually, for Minnesota to place him on the 15-day disabled list on Thursday.
Because of the sensitivity of the matter, Mauer was scheduled to travel to Baltimore on Friday to meet with his doctor. But after falling ill on Thursday, he visited the hospital, where after an extensive battery of tests to rule out any serious condition, he learned the that lingering viral infection was likely the cause of his sore legs.
"I think [it's less worrisome now], because when you start looking at all the different scenarios about whether his legs are going to be good enough and all those things, I think this tells you a lot more about where we're at, and why he's been so sore lately," Gardenhire said. "This started probably two or three days ago, and this helps us out. I think it eases everybody's mind knowing that he's got a viral infection, a flu bug-type thing, and we all know how you feel when you get that stuff. You add that into a little bit of soreness from baseball ..."
And you get panic centered around a fan favorite making $23 million during Year One of an eight-year deal worth $184 million.
Mauer will no longer fly ahead of the team to Baltimore, but instead will rest in St. Petersburg over the weekend and travel with the Twins on Sunday for Monday's series opener against the Orioles.
Even during all of Thursday's unknowns, general manager Bill Smith was optimistic that Mauer could rejoin the Twins in two weeks. On Friday, Gardenhire was more confident that timetable would stand.
"I hope so, yeah," Gardenhire said. "[Mauer] was going along pretty good, and feeling pretty good, until this last weekend ... and I think this probably tells us a little bit more about the virus and all that stuff. We feel pretty good about that now. We were a little concerned yesterday. Joe was, too, because he does nothing but want to play, he wants to get out there and play, and that's hard to do when you're aching all over the place and sore everywhere.
"This is a step in the right direction. Now we know where we're at, and we can handle it a little bit better and get him back on the baseball field."
This is the first time Mauer has been on the DL since 2009, when he missed the first month of the season with inflammation of the right sacroiliac (pelvic) joint. After he meets with his doctor on Monday in Baltimore, he'll return to Minnesota to begin his rehab process immediately.
Dawn Klemish is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.