The Mariners outrighted Diaz to Triple-A Tacoma on Monday.
Diaz will stick around in the Mariners organization after going unclaimed on waivers when he was designated for assignment Saturday. The 29-year-old lefty's stay on the 40-man roster and 26-man active roster lasted just three days, with Diaz allowing one run on two hits and no walks over 1.1 innings in his lone relief appearance.