One of the biggest questions that still remains as the Mariners approach the end of spring training is who will fill the fifth spot in their starting rotation to begin the regular season.

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Mariners general manager and president of baseball operations Jerry Dipoto made his weekly appearance on Seattle Sports 710 AM on Thursday morning, and he provided his insight on who is up for the spot and when a decision may be made.

While Dipoto had said earlier in spring training that one scenario the Mariners would explore was a trade for an experienced starter that could pitch toward the front end of the rotation, that’s looking less likely with opening day in Minnesota just a week away.

“I’m not encouraged by the the likelihood that it’ll happen, certainly before opening day,” he said about the possibility of a trade during Thursday’s Jerry Dipoto Show with Mike Salk. “And as I said in couching that (earlier in spring training), our preference was to find someone who pitches closer to the top or give our young pitchers an opportunity.”

And when it comes to that second option, Dipoto is encouraged by what the Mariners have seen from their options on the cusp of the major leagues.

“I think over the last week or 10 days, certainly the outings that you’ve seen from Matt Brash, from George Kirby, then what you haven’t seen on the backfields a couple of mornings ago with Levi Stoudt, these guys have pitched good to excellent,” Dipoto said. “Some of them have been eye-openers and we have a lot of momentum in camp with our own young arms, so we feel really good about the position we’re in whether or not we do acquire somebody.”

Brash and Kirby have been pitching in the same spring training games for the Mariners, and the two of them are the clear favorites in the battle for the fifth spot. Brash, who will turn 24 in May and is armed with an upper-90s fastball and wicked breaking pitches, has allowed no runs on just one hit and one walk in five innings of work this spring, striking out seven. The 24-year-old Kirby, whose calling card is elite command and control while also reaching the upper-90s, struggled in his first spring outing but looked great in three innings of work Sunday, striking out six while allowing no runs on three hits and a walk.

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So who has the edge? The two will each get a chance to make their case Friday night against the Rockies, but Dipoto said Brash, who was called up late last season by the M’s but didn’t appear in a game, goes into that game with an advantage.

“Matt has the upper hand because he was able to absorb a week of major league action at a high-leverage moment in our season last year,” Dipoto said, “so despite the fact that he didn’t get into a game, he knows what the environment is like when it’s at its best. And he’s been unbelievably composed this spring.”

That’s not to say Kirby is far behind, though, as Dipoto made clear when sharing what will ultimately go into Seattle’s decision about its rotation spot.

“(The choice will be) mostly just who we think is more prepared. And like with every other decision we make, that’s typically not about the physical stuff or the physical tools. It’s almost always about where we feel like the player is developmentally or emotionally,” he said. “I think you’ve seen in each of (Brash’s) outings, as well as with George, they just get better and better. And with George, it’s almost inning by inning. From the first inning he’s thrown until this last, it’s been an incredible growth period for him. With Brash, he went from being good to being a knockout.

“We’ll see both of them again on Friday, and the likelihood is we will determine from that day what our fifth starter position looks like.”

The Jerry Dipoto Show airs at 8:30 a.m. each Thursday on Seattle Sports 710 AM during The Mike Salk Show. You can hear this week’s edition in the podcast at this link or in the player below.

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