Moustakas was scratched from Tuesday's lineup with back spasms, Jeffrey Flanagan of MLB.com reports.
Moustakas was slated to start at third base and bat third for the Royals, per usual, but will instead nurse the injury. The severity of the issue is unclear at this point, and the 29-year-old should be considered day-to-day for the time being. Alcides Escobar will shift to third base with Adalberto Mondesi entering the lineup at shortstop.