Castillo (hamstring) is making good progress and has thrown off a mound, but he's not expected to return for the Mariners' series against the Astros to begin the week, Shannon Drayer of SeattleSports.com reports.

Castillo appears to be progressing consistently from his hamstring strain, and the Mariners remain cautiously optimistic he'll be activated when first eligible Monday, MLB.com reports. "Progressing as he should be," manager Dan Wilson said. "I don't think there's any expected date, right now, of his return, but progressing as he has. I know Luis is very diligent about getting his work in and trying to get healthy, and I think as far as we know right now, he's doing well."

Castillo was placed on the 15-day injured list Tuesday due to a Grade 2 left hamstring strain, Ryan Divish of The Seattle Times reports.

Castillo (hamstring) will undergo an MRI on his left hamstring on Monday in Seattle, Daniel Kramer of MLB.com reports.

Castillo was removed from Sunday's game against the Cardinals due to a left hamstring strain, Shannon Drayer of SeattleSports.com reports.

Castillo did not factor into the decision in Tuesday's loss to the Athletics, allowing two runs on four hits and a walk while striking out five over seven innings.

Castillo (10-11) got the win over the Mets on Sunday, allowing one run on four hits and two walks while striking out nine over six innings.

Castillo (9-11) took the loss Tuesday against the Tigers, allowing three runs on eight hits and no walks while striking out nine over six innings.

Castillo (9-10) picked up the win Tuesday against Boston, allowing three runs on six hits and a walk across six innings. He struck out four.

Castillo (8-9) picked up the win over the Angels on Thursday, allowing four hits and two walks over six shutout innings while striking out five.