The MRI that Castillo underwent Saturday revealed nothing more than fatigue in his inflamed right shoulder, Shannon Drayer of 710 ESPN Seattle reports.

EDGE Analysis

Since Castillo isn't dealing with any structural damage to his shoulder, the Mariners are optimistic that he'll be ready to return from the 10-day injured list when first eligible Aug. 30, or soon after. Until then, the Mariners are likely to turn to Drew Steckenrider and Paul Sewald as their primary options in save scenarios.