The Twins put Drew Butera at catcher for the game Wednesday night. Mauer's back tightened up before batting practice Tuesday, and he was scratched.
While he was criticized for missing too many games last season, Mauer has been one of the Twins' most durable players this year. He has played in 131 of a possible 142 games entering Wednesday, splitting his time among catcher, DH and first base.
Mauer's absence is a big break for the Royals and Wednesday's starter, Luke Hochevar. Mauer is hitting .355 for his career against the Royals and .519 against Hochevar.