Perez was sidelined by a strain on the right side of his chest. Perez, the MVP of the 2015 World Series, is hitting .278 with 21 homers and 65 RBIs in 99 games.
The Royals began the day just 1½ games back in the race for the second AL wild card.
To make room on the roster, rookie catcher Cameron Gallagher was optioned to Triple-A Omaha before Tuesday night's game against Colorado. Gallagher made his major league debut on Aug. 6 and hit .385 with one home run and five RBIs in five games with Kansas City.