SEATTLE -- Nick Margevicius and Ljay Newsome’s outlook to return in 2021 became far more bleak after each starting pitcher was placed on the 60-day injured list on Thursday, among a number of roster moves to make room for the debuts of outfielder Jarred Kelenic and pitcher Logan Gilbert.

Margevicius’ injury was classified as thoracic outlet syndrome, which can require surgery and an extensive recovery. It’s unclear if that’s the path that the left-hander will take. Newsome is also debating his options, including Tommy John surgery, after exiting his most recent outing on Saturday with what the Mariners classified on Thursday as a right UCL injury.

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Mariners general manager Jerry Dipoto indicated it’s a strong possibility both could miss the rest of the regular season.

“I'd say that's TBD on both guys, but obviously the fact that we moved into the [60-day IL] means that we don't think this is going to resolve itself anytime soon,” Dipoto said. “So, we hope to know more in the days ahead on both guys. They're both continuing to undergo testing and [get] multiple medical opinions … but right now that is certainly a possibility.”

The Mariners are down four starting pitchers in the first six weeks of the season (including Marco Gonzales and James Paxton), a huge blow for any team, but especially one that is closely governing the innings of its young staff.

That includes Gilbert, MLB Pipeline's No. 28 overall prospect. The right-hander was recalled on Thursday to make his first big league start against Cleveland.

Gilbert is a welcome -- and needed -- reinforcement, but he won’t have an extended leash, with an 80- to 85-pitch threshold for his debut. The Mariners are targeting roughly 110-120 innings for Gilbert for the rest of the season, and there’s a chance that the club could allocate him abbreviated starts of one to two innings to allow him rest while keeping his arm active, much like it did with Yusei Kikuchi in 2019. The intention is to keep Gilbert pitching through September.

“From mid-May through the end of the season, if we stay on turn with five-, six-inning starts, you're going to land right about that point,” Dipoto said. “And I'm sure that there'll be a time in there, we want to give him a little bit of a break.”

It’s not just Gilbert. Justus Sheffield and Justin Dunn have been around since 2019, but each is experiencing his first full big league season. Same for Chris Flexen, who topped out at 116 2/3 innings in Korea last season.

All of this is why the Mariners are adamant about sticking with a six-man rotation, even with the challenges that has placed on the bullpen.

“We don't think that the easy way to resolve it is by shortening up to a five-man rotation, frankly, because then we will do just the opposite of what we just set out to do -- we'll run out of innings with some of these young guys,” Dipoto said.

External options seem thin.

“There's no free-agent market, I'm aware of, that’s spawning starting pitchers in the middle of May,” Dipoto said. “They're just not out there. We did add in the offseason. We couldn't have predicted that we would have this kind of an injury issue.”

So Seattle will ride it out with what it has. That will likely mean more abbreviated outings of 50-60 pitches from Erik Swanson and Robert Dugger, both of whom are former starters and could be stretched out. Gonzales is throwing but is still at least a week away from doing so off a mound, Dipoto said. Jimmy Yacabonis and Héctor Santiago are veterans at Triple-A who are available in a pinch.

But for now, the Mariners will work with what they have.

Trammell also sent down
In order to make room for Kelenic, baseball's No. 4 overall prospect, outfielder Taylor Trammell was optioned to Tacoma, where he’ll get everyday playing time.

After playing his way onto the team with a stellar Spring Training, Trammell has struggled to a .157/.255/.337 slash line in 95 plate appearances over his first 27 big league games. But the Mariners are optimistic that there is still much good ahead for the 23-year-old.

“There’s a lot to like,” Mariners manager Scott Servais said. “He just needs to go play. He needs to play every day and continue to hone his skills because there's a lot to work with there. I’m excited about his future, but he learned a lot and he'll be back at some point.”

Other roster moves
• Right-hander Paul Sewald was recalled to give the bullpen a fresh arm. He last pitched on Monday and has thrown 4 1/3 scoreless innings with 10 strikeouts for Tacoma.

• Left-hander Aaron Fletcher was optioned to Tacoma one day after giving up three hits and one run in the seventh inning of a 7-1 loss to the Dodgers.

• Right-hander Wyatt Mills was optioned to Tacoma to clear a spot for a fresh arm after pitching three times during the five-game road trip.

• Outfielder Braden Bishop was designated for assignment. Bishop has been a clubhouse favorite and a defensive standout, but his bat hasn’t caught up to his glove at the big league level, where he has a .133/.188/.156 slash line in 47 games.