"The doctors have told me he's out 4-6 weeks, then he's going to have to throw and get himself ready," manager Lloyd McClendon said. "He's too valuable to rush back. We have to make sure he's at full strength when he does come back."
McClendon said Iwakuma, who finished third in the American League Cy Young Award voting last year after going 14-6 with a 2.66 ERA, will need to be able to throw six or seven innings and 85-95 pitches before he's ready for a regular-season game.
Building up to those levels usually takes pitchers five or six starts over the course of Spring Training, so Iwakuma's idea of getting ready in just three starts likely won't gain much traction with McClendon and new pitching coach Rick Waits.
"It would make me real happy if that was the case, but we'll see," McClendon said. "We'll do right by Iwakuma, that's for sure."
The Mariners were looking for another veteran starter even before Iwakuma's injury, so they could be in the market for another addition. Veterans Scott Baker and Randy Wolf have been given non-roster invites as they come off Tommy John surgeries, and former Angels starter Matt Palmer is in the mix as well.
Youngsters James Paxton, Taijuan Walker, Blake Beavan, Brandon Maurer and Erasmo Ramirez will also compete for starting jobs, and McClendon said he wants eight or nine pitchers getting stretched out through camp to fill the final five-man rotation.
"I'm always looking for eight or nine starters," he said. "Whether they're out there or Jack [Zduriencik] is going to acquire somebody else, I don't know. But I'm always looking. You always want to get better and you always want to have a surplus."
McClendon said Zach Miner, another non-roster veteran, has the ability to start and be a "swing-man" type pitcher, but will be looked at more as a reliever at this point.
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.