Tony Abreu, who delivered the game-winning hit in the Royals' 12-inning, 10-9 victory, was at third base instead of Moustakas, while Johnny Giavotella returned to second base. It's a one-day sit for Moustakas.
"It's a lefty, it was a long night last night, he's 1-for-19 on the trip," manager Ned Yost said. "He'll be back in there tomorrow."
Abreu's 0-2 hit to left field on Saturday night came on a pitch outside the strike zone.
"It wasn't even a strike, I saw the replay," Yost said. "Up and away."
Moustakas, by the way, is now the Royals' emergency catcher in case anything would happen to Salvador Perez and Brayan Pena during the course of a game.
"Moose caught in high school, Moose can do it," Yost said. "We talked about it a little bit yesterday."
That was infielder Chris Getz's designation before he went on the disabled list on Aug. 18 with a broken thumb.