Walker (foot) will begin a rehab assignment Monday with Triple-A Tacoma, MLB.com's Greg Johns reports.
Walker threw a bullpen session Friday without issue, and he has reached the final step in his recovery from his foot injury. It's not clear how many rehab starts Walker will make before rejoining the big club, but there is an outside shot he pitches for the Mariners next weekend, and he should be back in the majors by mid-August at the latest.