The Mariners recalled Diaz from Triple-A Tacoma on Friday.
Since being sent down to Triple-A, Diaz has allowed eight runs (six earned) in 11 innings across two starts. The 27-year-old allowed three runs to come across the plate during his spot start against the White Sox in June 11, and he'll presumably join the Mariners' rotation temporarily while Bryan Woo (hamstring) is on the injured list. Cody Bolton was optioned to Triple-A in a corresponding move.