Star Mariners right-hander George Kirby has been shut down from throwing due to shoulder inflammation and will very likely open the 2025 season on the 15-day injured list, general manager Justin Hollander announced to the team’s beat today (video link via Ryan Divish of the Seattle Times). There’s no structural damage at play, and Hollander made clear that Kirby felt he could continue pitching, but the team is understandably taking a cautious approach with such an important member of the pitching staff. Said Hollander:

“George Kirby has not been feeling great after his outings. In the outings, he’s throwing the ball well — same velocity as you would expect. He just hasn’t felt like he’s bouncing back great. We did an MRI — MRI looks great. No structural concerns whatsoever, and I will repeat that: zero structural concerns. There is some inflammation in there that we need to get out, so much to George’s chagrin, we are going to take the ball out of his hands. … This is more like a week-to-week thing than a day-to-day thing. We just want to make sure we’re doing the right thing for the big picture of the whole season as opposed to worrying about Opening Day.”

Hollander didn’t paint the issue as one that would require a long-term absence, but it’s nevertheless a cause for concern and a blow to the team’s short-term outlook. Kirby, the 20th overall pick in the 2019 draft, made his big league debut in 2022 and immediately cemented himself as one of the sport’s most promising young pitchers. The now-27-year-old righty has pitched 511 2/3 innings in the major and turned in a 3.43 ERA with a solid 23.3% strikeout rate and a minuscule 3.1% walk rate. He has arguably the best command of any pitcher in MLB and has parlayed that into an All-Star appearance and a top-10 Cy Young finish in his young career.

Kirby has never been on the major league injured list, though Divish notes that he missed a month during the 2021 minor league season due to mild inflammation in his shoulder and also had a bout of inflammation while pitching at the Mariners’ alternate site during the shortened 2020 season. Neither instance proved to be a long-term issue, and the M’s are surely hopeful that’ll be the case this time around as well.

There’s no immediate timetable for Kirby’s return. In his absence, Seattle will still have an outstanding top-four consisting of Logan Gilbert, Luis Castillo, Bryce Miller and Bryan Woo. Righty Emerson Hancock is the most experienced depth option on the 40-man roster, although the former No. 6 overall pick (2020) hasn’t yet lived up to that draft billing. He’s pitched in the majors in each of the past two seasons and delivered 72 1/3 innings with a 4.71 ERA. Hancock’s 7% walk rate is strong, but his 14.3% strikeout rate ranks seventh-lowest among the 449 pitchers with at least 70 combined innings over the past two seasons.

Other depth options in camp include righty Blas Castano, who’s also on the 40-man roster (but has not yet made his MLB debut) and non-roster invitees Logan Evans, Jhonathan Diaz, Luis F. Castillo and Casey Lawrence. Evans is generally ranked within the top 10 of an absolutely stacked Mariners farm system after posting a 3.20 ERA in 107 Double-A innings last year. He’s not far from being MLB-ready. Diaz and Lawrence are journeymen who’ve both had brief stints with the M’s in the past. Castillo made a brief MLB debut with the 2022 Tigers and has since spent two seasons in Japan, pitching to solid results.

For all the accolades heaped on their top-five starters, the Mariners are relatively light on depth options behind that prized quintet. It’s difficult to convince veterans who settle for minor league deals to sign on with a team that pretty clearly lacks a path to the majors, as exemplified by the Mariners and Phillies in recent seasons. The M’s generally need to rely on in-house development for depth. Hancock and Evans are products of that process, but the Mariners have also seen prospects like Taylor Dollard and Sam Carlson derailed by injury and traded others like Adam Macko, Connor Phillips, Brandon Williamson and Levi Stoudt in recent years.

It seems unlikely the Mariners would immediately go outside the organization for any sort of notable addition. Beyond the fact that Kirby doesn’t appear ticketed for a long-term absence, the M’s have scant payroll space, as their bare-bones offseason made abundantly clear. Beyond that, any new arms brought into the fold might not be built up in time to factor into the Opening Day rotation.

One route the team could take would be opportunistically grabbing a rotation arm off waivers if the opportunity presents itself, or scooping up a veteran who’s been in camp with another club but is informed he won’t make that team’s Opening Day roster. There aren’t any immediate options available in that regard, but as teams begin to set their rosters in the weeks ahead, both avenues can become more viable paths for Seattle to bolster its depth.