The Mariners designated Diaz for assignment Saturday.
Diaz gave up one run on two hits and struck out a batter in 1.1 innings during his lone appearance with the Mariners on Thursday. He'll now lose his spot on both the active and 40-man rosters to make room for the addition of top prospect Kade Anderson to Seattle's rotation. Diaz carries a 6.22 ERA through 111.1 innings at Triple-A Tacoma and is likely to remain there for the rest of the year if he clears waivers.