Washington Nationals right-hander Cade Cavalli, the team’s top prospect who was expected to join the rotation at some point this season, will undergo Tommy John surgery.

Cavalli, 24, was diagnosed with a Grade 3 UCL sprain and will be lost for the season, the team announced Thursday.

A first-round draft pick out of Oklahoma by the Nationals in 2020, Cavalli needed just 44 minor league starts over two seasons to find his way to the major leagues. He had a disappointing big league debut in August, giving up seven runs on six hits and two walks against the Cincinnati Reds. He didn’t pitch again with shoulder inflammation.

Cavalli is among a group of highly regarded Nationals pitchers that are close to emerging after the team’s rebuild following their 2019 World Series title. Cavalli, Josiah Gray and MacKenzie Gore are expected to form the core of the Nationals rotation of the future.

In 20 starts at Triple-A Rochester last season, Cavalli went 6-4 with a 3.71 ERA and 104 strikeouts with 39 walks in 97 innings.