It was supposed to be Walker's third rehab stop in as many cities after missing all of Spring Training recovering from shoulder inflammation. While in the training room Tuesday, Walker told Rainiers personnel that his shoulder "felt a little stiff."
Mariners general manager Jack Zduriencik said the club will reevaluate Walker on Wednesday before making any decisions about his future.
"He just says he felt stiff," Zduriencik said. "What you don't know about this is if you sleep on it wrong or however things work like that. When a guy's stiff and he's a guy like this you just figure let's take as many precautions as we can."
In late February, Walker, 21, was shut down from throwing activities for a week after he complained of shoulder soreness. He was diagnosed with inflammation in his shoulder's bursa sac. Walker gradually rehabbed during Spring Training before making his season debut April 4 at Class A High Desert, where he gave up four hits and one earned run in 4 1/3 innings while striking out seven.
Last week with Double-A Jackson he took another step, pitching five scoreless innings and striking out 10 while walking just one. On Tuesday, Walker was scratched before he began throwing. Zduriencik said the 6-foot-4, 230-pound Louisiana native felt great during his Monday workout.
"You're talking about a long season and a long career, so as much as we'd like to see him out here -- we're all excited about it -- but if he's out here the next day or two days from now, we'll continue to progress as scheduled," Zduriencik said.
Afterward, Walker didn't speak with reporters. Meanwhile, Zduriencik intimated the top prospect in the organization is day to day.
"Well, you always evaluate the next day because who knows," Zduriencik said. "He may walk out of here tonight feeling good, once he gets in there and gets stretched out. ... He may say 'Hey I feel great tonight,' walk in tomorrow and say, 'Oh, I feel terrific.'"
Last season, Walker made his Major League debut in late August and went 1-0 with a 3.60 ERA in 15 innings of three starts. The Mariners expected Walker to begin the year in the starting rotation. Now, they wait and hope his latest setback is minor.
"There could have been a lot of reasons for it," Zduriencik said. "Let's just wait and see tomorrow."
Adam Lewis is an associate reporter for MLB.com.
This story was not subject to the approval of Major League Baseball or its clubs.