In a concerning development for one of their highest-rated prospects, Orioles left-hander D.L. Hall will likely miss the rest of the season after being diagnosed with a stress reaction in his left elbow, general manager Mike Elias said Friday. Hall, 22, had already been sidelined at Double-A Bowie by what was first described as elbow tendinitis since June 12.

But Hall experienced a setback when, after resuming a throwing program recently, imaging revealed the stress reaction.

“This is going to require more rest,” Elias said. “I'm very pessimistic that he's going to be able to return this season. So again, that's something that we're going to have to look at when we get to the end of the fall, about what we want him to do in the offseason. It's probably going to be a situation where we're looking to rest him and platform him as best as possible for 2022.”

If the issue does end his season, Hall, the club's No. 4 prospect, will enter 2022 having thrown just 31 2/3 official innings since 2019. He pitched 80 2/3 innings in ’19, missed '20 to the pandemic, and went 2-0 with a 3.13 ERA in seven starts this spring at Double-A Bowie.

The former first-round pick was part of a forming super-battery down at Bowie with fellow top prospects Adley Rutschman and Grayson Rodriguez, flashing an upper-90s fastball, two distinct breaking balls and improved command before the injury. He compiled 56 strikeouts and walked 16 in his seven starts at Bowie, showcasing the upside he’s had since the Orioles drafted him 21st overall in 2017.

That upside remains obvious, but the elbow issue does spark questions about Hall’s long-term durability. He also dealt with lat issues in 2019; given the lack of innings, Hall’s big arm might signal a future more as a high-end reliever. That sort of role would also accelerate his big league ETA, in all likelihood. Hall could also be a candidate to pitch in the Arizona Fall League this year if he’s healthy and the Orioles decide they want him to make up for lost innings.

Also from the trainer’s room

Hall’s injury is just one of the many to be found up and down the Orioles’ organization. Nine of the Top 30 prospects are currently on the injured list or inactive, including six of their top 11. The club also has eight 40-man players on the IL, even after activating Anthony Santander on Friday.

To that end, Elias said left-handers Bruce Zimmermann (left biceps tendinitis) and Zac Lowther (left shoulder strain) would begin rehab assignments this weekend -- Zimmermann at High-A Aberdeen on Saturday and Lowther in the Florida Complex League. He also provided the following updates:

• No. 23 prospect SS Anthony Servideo had surgery to repair a sports hernia this week, the operation likely sidelining him for the rest of the season. The O’s third-round pick in 2020, Servideo played 20 games for Low-A Delmarva in his first pro season, hitting .246 without a homer but with a .489 OBP and an .801 OPS.

• No. 8 prospect OF Yusniel Diaz (right turf toe) resumed baserunning activity at Triple-A Norfolk. Diaz has been out since July 11; he’s played in just 27 games this season due to toe and groin issues.

• The team will look to get No. 10 prospect SS Terrin Vavra (back strain) in rehab games by Aug. 10, and to Double-A Bowie by the middle of the month, per Elias. Elias called Vavra an AFL candidate, also.

• No. 11 prospect SS Adam Hall landed on the IL at High-A Aberdeen with a quad strain. He could return by mid-August, per Elias.