Walker was optioned to Triple-A Tacoma on Monday, Shannon Drayer of MYNorthwest.com reports.
Walker struggled in his first outing after returning from a foot injury as he allowed six earned runs over just four innings. He had a poor showing in his rehab start at Tacoma as well when he gave up two runs over just 4.1 innings. With Walker being optioned, Seattle will bring Arquimedes Caminero up to The Show.