"It was just a little soreness, but I'm fine. I'm ready to go," Walker said Sunday. "I think I started a little early. I wanted to try to get a head start, but that's not going to happen."
The hard-throwing 21-year-old threw on flat ground Sunday and is expected to take the mound Monday, as is ace Felix Hernandez. All the other pitchers in camp have already thrown at least one bullpen session, but Hernandez typically starts a little slower.
Now Walker is on the same slightly delayed schedule, which certainly is no problem as far as getting ready for game action. The Mariners' biggest challenge may be holding Walker back, so he paces himself this spring.
"He's probably a little frustrated, because he's like a bull in a china shop," manager Lloyd McClendon said of the youngster's delayed start. "But he's fine. He's doing well."
The Mariners first Cactus League game is Feb. 27, and the regular season begins March 31. Thus Walker has six full weeks to make his case to be included in the rotation. And he knows exactly what he needs to work on.
"My biggest focus this spring is my offspeed pitches," he said. "I want to come out of spring with my offspeed ready to go. Last year in Double-A, it took me a couple weeks to get my offspeed stuff back, so hopefully I can come right out of spring with all my pitches ready to go.
"I think my curveball will be the biggest thing for me. My cutter, I feel already really comfortable with, and my changeup is OK."
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.