Walker has yet to pitch in the Majors this season after dealing with a sore right shoulder for much of the spring. He's 0-1 with a 9.00 ERA in two rehab starts for Tacoma after giving up just one run and one hit Tuesday, but dealing with control issues in El Paso.
Manager Lloyd McClendon said he would have a discussion with general manager Jack Zduriencik later Wednesday about who will start Monday's final game of the upcoming series at Tampa Bay, which currently would line up as Ramirez's next start.
"Taijuan didn't throw very well," McClendon said. "I'll talk to Jack today and see what happens. We've got an off-day tomorrow and a chance to rest some guys, and then we'll see where we go from there."
Hisashi Iwakuma could throw Monday on normal rest thanks to the off-day, but that would only delay the need for another starter until Tuesday, when Seattle opens a three-game series with the Yankees at Safeco Field.
Walker clearly isn't the answer yet, as McClendon said he'd still need one or more rehab starts to get ready.
"My understanding is he's healthy, he just pitched [poorly]," McClendon said. "That's the way it goes."
The Mariners are also waiting on rookie southpaw James Paxton, who is in Seattle rehabbing a sore left shoulder after his own Tacoma rehab process was halted after his first start following a six-week absence due to a strained left lat muscle. Paxton hasn't started throwing again yet, however, and he's going to need to build strength back up as well once he's cleared.
"He's progressing well. No setbacks," McClendon said. "We'll see where he is when we get home."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.