McClendon said veteran right-hander Chris Young will start Sunday's series finale in Anaheim, with rookie southpaw Roenis Elias facing the Mets when Seattle opens a seven-game homestand on Monday, July 21.
But McClendon said his fifth starter -- which was expected to be Walker -- was still not determined. The 21-year-old was sent down to Triple-A Tacoma to make two starts to stay fresh over the break, but his manager didn't sound pleased with Walker's approach after he threw five innings in a 7-2 victory over Fresno on Saturday night.
Walker allowed four hits with one run, one walk and one strikeout in that contest and is slated to pitch again Thursday in Reno. That would line him up to return the following Tuesday against the Mets on normal schedule, but McClendon wasn't in the mood to praise Walker when asked about what appeared to be a pretty good start for the youngster.
"I guess I see things differently than most people," McClendon said. "I don't see that as a good outing. Five innings, 83 pitches and one strikeout, that's not a good outing to me. And I'm not trying to bash the kid.
"But how we go about our business and the level of expectations from the Minor Leagues all the way up to the big leagues, it's got to change. Five innings, 83 pitches, one strikeout, that's not a good outing. I'm sorry. Not for me. And you can write it. I'm sure his agent will be calling, mad at me. But we've got to do better."
Walker was expected to challenge for a rotation berth coming out of Spring Training but missed considerable time with a sore shoulder. He was finally called up from Tacoma at the end of June and went 1-1 with a 3.60 ERA in two starts before being sent back down Wednesday rather than make his expected start Saturday against the A's.
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.