Diaz will be placed on the bereavement list by the Mets on Saturday, Mike Puma of the New York Post reports.
Diaz didn't appear in Friday's win over the Nationals, and he'll miss between three and seven games following the death of his grandfather. He'll reclaim his role as the Mets' closer once he rejoins the team, but Seth Lugo, Adam Ottavino and Trevor May are candidates for ninth-inning work during Diaz's absence.