Washington Nationals left-handed relief pitcher Sean Doolittle will undergo an internal brace procedure on his throwing elbow and will not return this season, he said Friday.

Doolittle is expected to be out for five to six months and aims to be ready for spring training in 2023.

“There’s too much instability being caused by that UCL not being healed enough and not being strong enough,” Doolittle told reporters. “At this point, I just want to go in and get it fixed. I want to get to the root cause of it and get it taken care of.”

The procedure is less invasive than Tommy John surgery, which requires a full reconstruction of the UCL (ulnar collateral ligament).

Before being placed on the injured list in April, Doolittle pitched in six games for Washington, allowing one hit and no runs over 5 1/3 innings with six strikeouts and no walks.

The two-time All-Star (2014, 2018) returned to the Nationals in free agency ahead of the 2022 campaign. During his first stint with the club (2017-20), he helped Washington win its lone World Series.

Doolittle started his career with the Oakland Athletics (2012-17) and spent 2021 with the Cincinnati Reds and Seattle Mariners. In 463 career relief appearances, he has gone 26-24 with a 3.20 ERA and 112 saves.

–Field Level Media