Joe Mauer out with back spasms
Manager Ron Gardenhire says Mauer's back tightened up on the field before batting practice.
Ryan Doumit took Mauer's spot behind the plate.
Mauer had played in 131 of a possible 141 games entering Tuesday. The All-Star played in just 82 games last season while battling leg and other injuries.
Mauer is hitting .319 this season and is a career .355 hitter against the Royals.
Copyright 2012 by The Associated Press
MORE MLB HEADLINES
- Trout hits for cycle as Angels drub Mariners
- Sandoval's HR caps Giants' rally past Nationals
- Quintana sharp as White Sox edge Red Sox
- Straily outduels Darvish as A's top Rangers