"I told him 'no matter what, you're out. You're going to sit today'," Gardenhire said.
Mauer entered the game in the 10th as a pinch-hitter and drew a walk to load the bases, after falling behind 0-2 against Royals reliever Bruce Chen. Mauer scored on Jordan Schafer's two-run single that broke it open as the Twins scored six times en route to an 11-5 win.
Mauer went 0-for-4 with two strikeouts in Minnesota's 6-1 loss on Wednesday. It was his first multi-strikeout game since July 1.
"I watched him last night, I thought he was dragging a little bit last night. He dove all over the place and about killed himself," Gardenhire said.
Mauer entered Thursday batting .288/.391/.475 in 16 games since returning from a strained right oblique that sidelined him for 34 games.
"He's going to have to have a break, he's not as young some of those other guys out there," Gardenhire said.
Jackson Alexander is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.