"I'm not sure what the number is for starts down there," manager Lloyd McClendon said. "I think it's four to five innings per start and hopefully we can get him up to 25-30 innings."
The Mariners considered having rookie southpaw James Paxton also pitch in the AFL, but opted instead to have him stay in Seattle and work out with the team's training staff over the winter as he also rebounds from an injury-shortened season.
Walker, 22, went 2-3 with a 2.61 ERA for the Mariners, saving his best for last as he closed the regular season with two strong outings in late September, including eight innings against the Blue Jays when he allowed just four hits and one run in a 1-0 loss in his final outing.
The Saguaros will host the Peoria Javelinas in their opener Tuesday at 12:35 p.m. PT at Surprise Stadium.
Walker is one of seven Mariners prospects playing for the Saguaros, who also have players from the Rangers, Padres, Reds and Red Sox.
Right-handers Matt Anderson, Matt Brazis and Stephen Landazuri join Walker on the Saguaros pitching staff, while catcher John Hicks and infielders D.J. Peterson and Patrick Kivlehan are also on the squad.
Peterson, the club's 2012 first-round Draft pick, is expected to get some work at first base as well as third as the Mariners would like to have him come to camp next spring and compete for the first-base job. Peterson is the No. 2 prospect for the Mariners in MLB.com's ratings, with Kivlehan at No. 6 and Hicks at No. 19.
Walker no longer is on the prospect rankings, having accumulated too much playing time in the Majors to qualify.
Each AFL team plays a 32-game schedule that concludes on Nov. 13, with a one-game AFL Championship on Nov. 15 for the top two finishers.
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.