Walker got the word after pitching five-plus innings in Wednesday's 3-2 loss to the Mets.
“I know there are things I need to work on,” he said. “I'd rather come up here at my best so I can come up here and stay up here. So go down there, get my work done and, hopefully, come back and at my best.”
Manager Lloyd McClendon plans to bring back Hisashi Iwakuma, who starts Thursday against Baltimore, on normal rest to pitch next Tuesday in Cleveland.
The Mariners are expected to replace Walker with a position player. They cleared space Wednesday for Walker by optioning Ramirez back to Tacoma after he pitched seven innings in Tuesday's 3-1 loss to the Mets.
Monday's open date means the Mariners won't need a fifth starter until Aug. 2 in Baltimore. If all goes as expected, left-hander James Paxton figures to reclaim that spot after nearly four months on the disabled list.
Paxton threw 60 pitches Tuesday over three innings in a rehab start at Tacoma in his recovery from a strained back muscle. He then threw 10 more pitches in the bullpen to build his endurance.
Barring setbacks, Paxton should throw 75-80 pitches in his next start at Tacoma, which would position him to step into the Aug. 2 slot against the Orioles.
If Paxton isn't ready, the Mariners could also opt for Walker or Ramirez. Both would be eligible to return from the minors by Aug. 2.
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