CLEVELAND -- A pitching staff that was remarkably healthy last year will weather another notable injury early, as Andrés Muñoz was placed on the 15-day IL with a right deltoid strain ahead of Seattle’s series finale against the Guardians on Sunday.

Muñoz last pitched on Friday, throwing a hitless eighth inning in his fourth outing of the year, and he hadn’t yet pitched on back-to-back days, a by-design effort to limit his workload after a slow ramp-up in Spring Training related to offseason surgery on his right foot and ankle.

“When you throw that hard, like there's this part of your shoulder that's got to allow you to slow it down, your decelerator, and that's what's bothering him,” Mariners manager Scott Servais said.

Servais suggested that Muñoz’s latest issue isn’t severe, but it’s nonetheless concerning given that he is Seattle’s highest-leverage reliever following a breakout 2022, when he became one of MLB’s best. Muñoz underwent imaging that didn’t reveal any structural damage, and he will spend the next few days resting.

Muñoz has averaged 100.8 mph on his four-seam fastball and 99.2 mph on his sinker, both fairly in line with his readings from last year, but the crispness of his slider has been an issue. It’s been more like a sweeper than the firmer, harder shape that Muñoz would like. He’s also noticed that he hasn’t been able to bounce back following outings as easily as he did in the past.

“It hasn't been easy for him, and we're playing the long game here,” Servais said. “We know for us to be really good throughout the course of the season, we need him, so the decision was just to give him a couple of weeks of downtime.”

The transaction also reshapes the scope of Seattle’s bullpen in the early going, which has already seen high usage from Matt Brash, Paul Sewald and Penn Murfee, the latter of whom has pitched in an MLB-high six games this season.

Brash, who made a highly successful transition from the rotation last season, will likely slide into Muñoz’s role against opposing lineups’ most challenging pockets. He’d already been used against those tough hitters, but usually earlier in games.

“We like running Matt through the middle or the top of most lineups, and he's done a great job. ... He's ready for that and is able to take that on,” Servais said. “And again, it'll all be predicated on who's available on this particular day.”

Here are the rest of the Mariners’ moves:

• Reliever Matt Festa optioned to Triple-A Tacoma
• Reliever Justin Topa recalled from Tacoma; reliever J.B. Bukauskas selected from Tacoma
• Evan White (Grade 2 left adductor strain) recalled and placed on 60-day IL

Festa has walked six of the 19 hitters he’s faced and surrendered four runs in three outings, so his situation is more about re-establishing command in the Minors. Topa and Bukauskas, on the other hand, should contribute immediately. Topa had a solid spring and was an odd man out in a bullpen that returned almost everyone from 2022. Bukauskas experienced some command issues, falling behind in counts, but finished spring strong.

“[Topa] can get you to hit it on the ground,” Servais said. “[He] has a really good sinker, the movement on the sinker is outstanding. That's probably his primary pitch to lean on. Bukauskas has all four pitches. The key thing with J.B. is you've got to get in the strike zone early. We've talked to him. I said, ‘If you want to stay with us all year, throw strike one.’”

They join lefty Gabe Speier as players who didn’t break camp with the team, but who will now have an opportunity. Speier has thrived in a small sample, including a few big moments in Saturday’s win, after taking the roster spot of Robbie Ray, who suffered a left flexor strain in his first start.

The Mariners suffered only a handful of pitching injuries last season -- none in their rotation -- and nearly all returned fine.

“Last year was an abnormality,” Servais said. “It's just what happens in baseball. You're going to have some guys get a little banged up. We felt good about our depth, and we got to Spring Training and saw that play out with guys, and now we're going to see it play out here at the Major League level. A lot of guys are going to get opportunities, and we need them to step up.”