Zych (shoulder) began a rehab assignment in the Arizona Rookie League on Friday, MLB.com's Greg Johns reports.
He gave up one unearned run but did not give up a hit while walking one over an inning Friday. Considering he is beginning the rehab assignment in the AZL, it could be a somewhat lengthy run through the Mariners' minor league affiliates before Zych is activated. He has electric stuff when he is healthy, but Edwin Diaz is the unquestioned closer for Seattle going forward.