CHICAGO — The worst-case scenario when Zach Eflin walked off the mound last week with the Orioles’ athletic trainer by his side has come true.

Eflin underwent Tommy John elbow reconstruction surgery with Dr. Keith Meister on Wednesday in Arlington, Texas, the team announced. He will miss the remainder of the season.

The right-hander, who also celebrated his 32nd birthday on Wednesday, opened the season as Baltimore’s No. 5 starter, but his presence in the rotation raised both the floor and ceiling of the group as a dependable veteran who received Cy Young Award votes only three years ago.

Eflin flew down to Dallas on Tuesday to receive a second opinion from Meister, the renowned surgeon who performs many elbow surgeries every season. Meister successfully repaired Eflin’s torn ulnar collateral ligament — the first elbow injury the right-hander has suffered in his 11-year MLB career.

Baltimore had already transferred Eflin to the 60-day injured list on Tuesday to make space for left-hander Nick Raquet, who was acquired in a trade with the St. Louis Cardinals. The Orioles then activated Raquet and optioned right-hander Brandon Young to Triple-A Norfolk following his spot start in their 2-1 win over the Chicago White Sox on Monday.

This is Eflin’s second straight season that has been derailed by injury. Last year, persistent lower back issues finally caught up to him, requiring surgery in August to fix a herniated disc in his spine. But Eflin looked like his old self this spring, pitching so well to win a rotation spot over Dean Kremer. Eflin was then dominant in his opening start against the Texas Rangers, striking out seven batters in 3 2/3 innings.

In the fourth inning, pitching coach Drew French made a mound visit. The next pitch was a curveball — Eflin’s slowest of the night — and he looked uncomfortable after releasing it. Athletic trainer Scott Barringer visited the mound, and Eflin walked off without throwing a test pitch. The injury was bad enough that Albernaz knew that night that Eflin would be placed on the IL the next day.

It’s a massive blow for Eflin, who re-signed with the Orioles over the offseason on a one-year, $10 million deal with a mutual option for the 2027 season. Baltimore originally acquired him at the 2024 trade deadline in a deal with the Tampa Bay Rays. The club sent three prospects for a then-established starter who had mixed success across his first seven seasons with the Philadelphia Phillies before taking a step forward in Tampa Bay.

He was brilliant for the Orioles down the stretch in 2024, posting a 2.60 ERA and 1.12 WHIP in nine starts despite missing two weeks with shoulder inflammation that August. Eflin then took the ball in Game 2 of their wild-card series against the Kansas City Royals and again as their opening day starter in 2025. His chronic back issue and a lat strain limited him to 14 starts, and he put up a 5.93 ERA before being shut down for good in August.

Eflin’s future with the organization is in much more doubt than it was after his back surgery. Tommy John surgery typically requires a recovery timeline of anywhere from 12 to 18 months, making the Orioles unlikely to exercise their side of his mutual option. He would be a candidate for a two-year deal in free agency this offseason should he progress well enough to make a second-half return possible, but Eflin has a long road ahead of him.

The Orioles have patched together the back end of their pitching staff in the days since his injury, calling up Young, Cade Povich and Albert Suárez to handle bulk innings. Meanwhile, injuries have struck in their bullpen, too, with left-hander Dietrich Enns (left foot infection) and right-hander Yaramil Hiraldo (right shoulder inflammation) both landing on the injured list.

Kremer will be first eligible to be recalled from Norfolk on Thursday, and he’s expected to step in as the Orioles’ full-time No. 5 starter once ready. He’s overqualified as far as No. 6 starters go, coming off a season in which he led Baltimore in innings (171 2/3) and wins (11) while posting a 4.19 ERA. Kremer has made at least 20 starts and finished with an ERA below 4.20 each of the past four years.

The Orioles already named Povich their starter for Sunday’s series finale against the Texas Rangers, making Kremer — who took the mound for his second Triple-A start Wednesday — a candidate to step into the rotation during the next turn. Povich made his season debut in Pittsburgh last weekend in relief of Chris Bassitt and allowed two runs on four hits and three walks over 5 2/3 innings.

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