The Mariners plan on sending Castillo (shoulder) to their rookie-level Arizona Complex League affiliate for a one-game rehab assignment before activating him from the 10-day injured list Saturday or Sunday, Corey Brock of The Athletic reports.

Because the Mariners are playing a three-game set in Arizona this weekend, the organization wants to keep Castillo nearby for his rehab assignment rather than having him report to a higher-level affiliate. Castillo has been sidelined for only a week and a half with the inflamed right shoulder, so one tune-up outing in the minors should be all he needs to prove to the Mariners that he's healthy. Once reinstated from the IL, Castillo should re-emerge as a factor in Seattle's closer picture.

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