That would put Iwakuma's return in mid-April in the best-case scenario, a few weeks into the regular season. He was projected as the No. 2 starter behind Felix Hernandez in the Mariners' rotation after going 14-6 with a 2.66 ERA last year.
Walker, 21, was also expected to open the year in the starting five if all went well, but the young right-hander -- ranked as the No. 6 prospect in baseball by MLB.com -- arrived at camp with a sore shoulder and was finally shut down for a week on Friday after tests showed inflammation.
Once they're cleared to throw, both hurlers will need to build up their arm strength through the normal spring program that other pitchers have already been doing for more than two weeks.
McClendon estimated Iwakuma would need to throw about 20 innings in simulated or Minor League games before he could start in a regular-season game, and that would only come after the normal progression of flat-ground throwing and bullpen sessions.
"I think it'd be hard-pressed for those guys to pitch Opening Day, or the second or third day," McClendon said. "One of the problems we face, we don't have any days off early. We play seven in a row. So speaking realistically, I think it would be tough, yeah."
Iwakuma initially was told he'd need to keep his splint on for four-to-six weeks after injuring his finger just prior to the start of camp. There was some hope that he was ahead of schedule after doing mound work and drills without gripping a ball, but Friday's re-examination led to the instructions to keep the finger immobile for another three weeks.
"I was honestly disappointed and frustrated at the same time, but you have to respect what the doctor says," Iwakuma said through translator Antony Suzuki. "I was ready to play catch today. It is what it is and I'll just have to wait three more weeks."
Iwakuma said his finger is feeling better, but Dr. Donald Sheridan, one of the top hand specialists in the country, believed it would be best to stay on the long side of the original estimate.
"That's what was diagnosed the first time, so it was not a surprise," McClendon said. "Am I disappointed? Yeah. But at the same time, we've got to get him healthy. We can't rush this thing. The doctors have assured us this is the right thing to do, so we need to keep working forward with it. I know he is a little disappointed, but it's the right thing to do for his future."
Those are largely the same words spoken a day earlier when Walker's shutdown was announced. But McClendon isn't changing his optimistic outlook despite looking at opening the year without two of his top hurlers.
"I always plan for the worst, and our contingency plan has been that," he said. "This gives other guys opportunities to go out and see what they can do. So we'll see what happens."
How soon does Iwakuma think it'll take to get ready once he's cleared to grip a ball again?
"That's a tough question because I've never been in this situation before," he said. "Obviously I want to get back as soon as possible, so hopefully within a week or two I'll be able to throw hard and we can go from there."
Iwakuma was strong from start to finish last year in his first full season in the Mariners' rotation, pitching a career-high 219 2/3 innings and finishing third in the American League Cy Young Award voting. He set a club record with his 1.006 WHIP and ranked third in the league in ERA and opponents' batting average (.220).
The likelihood of starting the season on the disabled list is difficult, but Iwakuma said he'll maintain his conditioning with extra weight-room work and "shadow" drills on the mound where he goes through his throwing motion without a ball, wrapping a towel around his hand instead.
"It is very disappointing, but you can think about it and not go anywhere," Iwakuma said. "So you just have to move forward and come back as soon as possible and make sure I don't have any setbacks from coming back too quick. That's all I can think of right now, going forward."
Scott Baker and Randy Wolf, two veteran rotation candidates coming back from 2012 Tommy John surgeries, are scheduled to make their spring debuts on Saturday and Sunday. The Mariners also have young prospects James Paxton, Erasmo Ramirez and Blake Beavan competing for jobs, along with non-roster invitees Matt Palmer and Mark Rogers.
One thing seems certain: You can ticket Hernandez in to make his club-record seventh Opening Day start on March 31 in Anaheim.
"Unless you've got somebody else," McClendon said with a laugh. "I'll try to see if he can go Opening Day, second day and the third day."