Castillo (shoulder) felt good after throwing a bullpen session Monday, though he's expected to need a rehab outing before returning from the injured list, Daniel Kramer of MLB.com reports.

EDGE Analysis

The Mariners previously expressed optimism that Castillo could return after spending the minimum 10 days on the injured list, but that won't be happening, as that window expired Monday. It doesn't look as though he'll miss too much more time, but he'll miss at least a few more days if the Mariners do indeed go ahead with the rehab assignment.