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.
"They got the [impact test] results back," Yost said. "And he got the approval from MLB and the Players Association."
As expected, the Royals sent catcher Francisco Pena back to Triple-A Omaha and replaced him with catcher Drew Butera.
"A good catch-and-throw guy," Yost said of Butera. "It always used to bother me when he was in the game [with the Angels] because he's got such a good arm, it would neutralize our running game."
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.