Santos, who was activated from the injured list Sept. 23, subsequently made two relief appearances during which he fired two scoreless innings while allowing one hit and recording one strikeout.

The Mariners reinstated Santos (biceps) from the 15-day injured list Monday, Daniel Kramer of MLB.com reports.

Santos (biceps) continued his rehab assignment with Triple-A Tacoma with one-inning scoreless appearances on Wednesday and Saturday, allowing one hit and two walks while recording a strikeout over that span.

Santos (biceps) fired two-thirds scoreless innings in Triple-A Tacoma's loss to Oklahoma City on Sunday, issuing two walks and recording a strikeout.

Santos (biceps) allowed an earned run on a walk over two-thirds of an inning in Triple-A Tacoma's win over Oklahoma City on Friday. He struck out two.

Santos (biceps) fired a scoreless sixth inning in Triple-A Tacoma's extra-inning loss to Oklahoma City on Tuesday, allowing two walks and recording a strikeout.

Santos (biceps) started his rehab assignment with Triple-A Tacoma against Albuquerque on Friday, firing a scoreless eighth inning during which he allowed a hit and a walk.

Santos (biceps) has begun throwing at the Mariners' extended spring training in Arizona but remains without a timetable for return, MLB.com reports.

The Mariners placed Santos on the 15-day injured list with right biceps inflammation Friday, retroactive to Thursday.

Santos exited Wednesday's game versus the Red Sox due to a bicep injury, Daniel Kramer of MLB.com reports.