SEATTLE -- Mariners general manager Jerry Dipoto talks glowingly about the ace potential of James Paxton , the durability and capability of Mike Leake and Erasmo Ramirez , and the upside of young starters Marco Gonzales , Andrew Moore and Ariel Miranda .

Fans may question what he sees as the strength of the returning rotation, but Dipoto firmly believes that group will more than hold its own in the American League battles this season.

One concern he does share, however, is the health of Felix Hernandez . If there is an unknown in this starting staff in Dipoto's eyes, it centers largely around just how much the Mariners can get out of their former AL Cy Young Award winner after an injury-wracked 2017.

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"Nuts and bolts, it comes down to how Felix comes in in Spring Training," Dipoto said on Thursday at the team's pre-Spring Training media luncheon. "If Felix can give us the 25 starts or more that he gave us in 2016, we're going to be a good team.

"If Felix gives us 16 or less, like was the case last year, we're going to have to answer a lot of questions. I wish I knew the answer to which of those it is. I don't. But we're going to find out pretty quick."

Hernandez is two years removed from going 18-9 with a 3.53 ERA in 31 starts and pitching 200-plus innings for an eighth straight season. In '16, he slipped to 11-8 with a 3.82 ERA over 153 1/3 innings in 25 starts after missing six weeks with a strained calf.

Last year, the 31-year-old went just 6-5 with a 4.36 ERA in 86 2/3 innings over 16 starts while missing three months on two DL stints due to shoulder issues. But with two years and $54 million plus an option year for 2020 still remaining on his contract, the Mariners are hopeful Hernandez can at least bounce back to his '16 level.

Manager Scott Servais said Hernandez will take a different approach this spring. In the past, the veteran right-hander started throwing later in camp than the rest of the pitchers, and he would only have a couple of Cactus League outings to help preserve his arm for the long haul of the regular season. But no more.

"Felix isn't coming off a 200-plus inning season," Servais said. "He'll go through more of a normal Spring Training, and I think it'll be important for him. Felix is so talented and has had so much success that with his ability to just turn up the dial from one to 100, he could do that within the last 10 days of spring. That's not the case anymore as you get older."

Though veteran starters like Yu Darvish , Jacob Arrieta , Lance Lynn and Alex Cobb remain available on what has been a sluggish free-agent market, Dipoto reiterated the Mariners have committed to Paxton, Leake, Hernandez and Ramirez. He would like to use the fifth-starter spot to develop a young, cost-controllable starter like Gonzales, Moore or Miranda for the long-term benefit of the franchise rather than lock big money into another long-term deal.

"We have to create innings for these guys to show us what they can do," Dipoto said. "Because if you can get one of those guys to step forward, truly, the way we believe they can, when that clicks, now you have young affordable starting pitching that you can grow with."

Dipoto believes Gonzales and Moore have much more to offer than what was seen last year in their limited late-season time.

"You just won't know if you're going off 35 innings in a comeback season from Tommy John [like Gonzales] or the first 50 innings of a career that took you from Oregon State to the big leagues in under two seasons [like Moore]," he said.

"We're doing the best we can to develop our system, not to clog it. Could we go out and sign a free agent that would be better than our current fifth starter? Absolutely. Would that be the best thing for the present of the Mariners? Maybe. Would it be best through the wider lens for the present and future of the Mariners, probably not."

And if it doesn't work out with Hernandez or the youngsters? Dipoto noted he's never been shy about making trades or changes if things don't go as planned.

"We'll be able to address those needs as we go," he said. "Because the one thing we've not had to deal with here is a lack of resources."