Chicago Cubs pitcher Justin Steele will undergo season-ending surgery to repair the flexor tendon in his left elbow, manager Craig Counsell told reporters Sunday.

It was unclear whether Steele, who underwent Tommy John surgery in 2017, will need another full ligament-replacement procedure or a Tommy John revision with an internal brace. The 29-year-old left-hander will be sidelined until 2026.

"On a day like this, you feel for Justin," Counsell said before Sunday's series finale against the Los Angeles Dodgers. "It's kind of the life of a major league pitcher, these injuries that make you miss most of seasons.

"But I talked to him this morning, and he has a great attitude about it, as he always does. He knows that it's part of the career he's chosen, and he's going to take it a step at a time and do the best he can to come back even better."

Steele was placed on the injured list last week after feeling discomfort in his elbow following his last start. He threw seven shutout innings against the Texas Rangers on Monday but still felt pain after arriving at the stadium the next day for treatment.

He was 3-1 with a 4.76 ERA in four starts before going down.

Steele has had a history of minor elbow problems over the past couple of seasons, spending time on the injured list in each of them, including late last year before returning for two September outings. He started the second game of the season for the Cubs against the Los Angeles Dodgers in Japan last month.

Overall, Steele is 32-22 with a 3.30 ERA in 91 career starts, all with the Cubs.

The injury opens a huge hole in the team's rotation. Long reliever Colin Rea will take Steele's place in the rotation on Sunday night.

Counsell said right-hander Javier Assad, who will begin a minor league rehabilitation assignment with Triple-A Iowa on Tuesday, will be a candidate to fill Steele's spot when he returns from a left oblique strain. The team has several other in-house candidates who could also get a look, including lefty Jordan Wicks and righty Cade Horton.

Horton is one of the Cubs' top prospects but is still working back from an injury that kept him out of action last year. The team could also look to a possible trade, as Miami Marlins righty Sandy Alcantara is likely to be on the market this summer.

The Associated Press contributed to this report.