Hisashi Iwakuma's MRI revealed a Grade 1 lat strain and he will miss 2-to-4 weeks.
Mariners placed RHP Hisashi Iwakuma on the 15-day disabled list, retroactive to April 21, with a strained lat muscle.
Hisashi Iwakuma turned in his third consecutive mediocre start, giving up four runs in 5 1/3 innings in Monday's loss to the Astros.
Hisashi Iwakuma allowed four runs in five innings, taking a no-decision in Tuesday's loss to the Dodgers.
Hisashi Iwakuma allowed five runs (four earned) in six innings during Wednesday's loss to the Angels.
Hisashi Iwakuma didn't throw any splitters during a two-inning minor league appearance Thursday due to a blister he developed in a March 28 outing.
Hisashi Iwakuma gave up four runs in five innings as the Giants held on for a 9-8 victory over the Mariners on Saturday.
Hisashi Iwakuma will make his next scheduled start Thursday in a simulated game against minor leaguers.
Hisashi Iwakuma tossed two perfect innings in Saturday's loss to the Diamondbacks in the Cactus League.
Hisashi Iwakuma indicated Sunday that he's not interested in returning to Japan to pitch when his contract expires after the 2015 season.
Mariners general manager Jack Zduriencik said trading Hisashi Iwakuma "wouldn't make any sense."
Nick Cafardo of the Boston Globe reports that the Mariners have "fielded inquiries from a few teams" on Hisashi Iwakuma.
Mariners exercised RHP Hisashi Iwakuma's $7 million club option for 2015.
Hisashi Iwakuma won Friday after allowing two runs in 6 1/3 innings against the Angels.