Mauer will have dye injected in his lower back and have a magnetic imaging arthrogram so doctors can try to figure out what's causing the discomfort, the St. Paul Pioneer Press reported Tuesday.
The 25-year-old all-star has had the soreness since late October and had surgery in late December to remove a kidney blockage that was thought to be the root of the problem. But he's been slow to recover and it has severely limited his participation in spring training in Florida. He's been limited to light conditioning and agility drills, and short sessions catching or in batting cages.
"He's not able to consistently go out and do anything," Twins Manager Ron Gardenhire said.
"We haven't been able to get him back on the field, so to say we're not concerned would be silly. We've got to figure out what's going on so we can get him back on the field. This is another effort to try to figure out where we're at."
With Opening Day a month away, the Twins have time. But if the .317 lifetime hitter can't go, they will start Mike Redmond and use their inexperienced prospects as backup.