Dunn (shoulder) was sent back to Seattle for an MRI on Friday and will not pitch again this season, Corey Brock of The Athletic reports.
Dunn was working his way back from a shoulder strain that has kept him sidelined since mid-June. He threw just four pitches in a rehab game for Triple-A Tacoma on Thursday before exiting with an apparent setback, the severity of which should become clear following his MRI.