"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.