The Mariners designated Diaz for assignment Friday, Adam Jude of The Seattle Times reports.
With Cooper Criswell coming over from the Mets in a trade, Diaz will give up his place on the Mariners' 40-man roster. The 29-year-old southpaw made just one appearance with the Mariners near the start of the 2025 regular season, allowing one hit and striking out one batter over 1.1 innings. He spent the rest of the season at Triple-A Tacoma and turned in a 4.15 ERA and 1.32 WHIP across 138.2 frames.