Mariners right-hander Hisashi Iwakuma felt discomfort in his surgically repaired shoulder during a sim game on Sunday and will be temporarily shut down from throwing, Ryan Divish of the Seattle Times reports on Twitter. The Mariners are hopeful it’s merely tendinitis, but regardless, it’ll delay Iwakuma’s attempt to return to the majors.

The 37-year-old Iwakuma’s latest problem is particularly alarming after shoulder troubles helped limit him to a career-low 31 innings of 4.35 ERA/6.42 FIP pitching in 2017. He ended up undergoing arthroscopic shoulder surgery in late September, just over a month before the Mariners declined his $10MM option for 2018. Iwakuma quickly returned to the Mariners on a minor league deal with the hope that he could work his way back to the majors by May. That may now be in serious jeopardy in light of Sunday’s developments.

Although Iwakuma scuffled through last season, his Mariners tenure has been a resounding success since he emigrated from Japan prior to the 2012 campaign. Iwakuma has recorded a 3.42 ERA/3.87 FIP in 883 2/3 innings, and the Mariners would certainly welcome that type of production from him this season if he makes it back to the mound.

Seattle, a prospective playoff contender, has gotten off to a quality 15-11 start without Iwakuma, though its rotation hasn’t been great in the aggregate. Entering Sunday, Mariners starters rank last in the majors in ERA (5.73) and fourth from the bottom in fWAR. The M’s top three starters – James Paxton, Felix Hernandez and Mike Leake – each figure to perform better as the year progresses, but the team’s rotation could still feature multiple question marks even if that happens.