Seattle Mariners right-hander Matt Brash underwent Tommy John surgery on Wednesday and will be sidelined for at least part of the 2025 season, general manager Justin Hollander told reporters prior to Friday's home game against the Oakland Athletics.

Hollander said the UCL was repaired and a brace was installed in Brash's pitching arm.

"We anticipate 12 months and back at it, so hopefully June of next year he'll be back and ready to go," Hollander said. "This is a tough one. Usually I don't give more detail than the injury."

Brash hasn't pitched this season and was shut down from throwing in late April.

Brash, who turns 26 on Sunday, led the majors with 78 appearances last season and went 9-4 with four saves and a 3.06 ERA.

"What he did last year was unbelievable how many times he came through for us," Hollander said. "... (He) was rapidly turning himself into one of the best relievers in the American League. To have the season go away like this stinks for him and stinks for us."

Overall, Brash is 13-8 with a 3.63 ERA in 117 appearances (five starts) in two seasons with Seattle.

The Mariners acquired Brash from the San Diego Padres on Sept. 17, 2020 to complete a nine-player deal in which Seattle scored big by landing first baseman Ty France and right-handed reliever Andres Munoz.

Seattle also activated right-hander Bryan Woo (elbow) from the 15-day injured list to start Friday night's game against the A's. Woo is making his first start of 2024 after beginning the season on the IL.

Last season, the 24-year-old went 4-5 with a 4.21 ERA in 18 starts.

The Mariners also designated right-hander Tyson Miller for assignment. Miller, 28, had a 3.09 ERA in nine relief appearances for Seattle this season.