Players on the bereavement list can be there for a minimum of three days and a maximum of seven.
Yost also said Christian Colon would fill in at third base during Moustakas' absence.
"[Orlando] Calixte could mix in there somewhere," Yost said, "but it will be Colon."
The Royals also announced that shortstop Alcides Escobar was activated from the seven-day concussion disabled list. Escobar sustained the injury after being hit in the helmet with a fastball from the Indians' Danny Salazar.