Diaz was added to the Mariners' spring training roster as a non-roster invitee.
Diaz was designated for assignment and outrighted to Triple-A in January, when the Mariners acquired Cooper Criswell. The left-hander will likely be a depth option for Seattle's bullpen this season, although he isn't guaranteed a spot on the Opening Day roster. He made just one big-league appearance in 2025.