Per MLB Network's Jon Heyman, Kahnle's operation was performed by Yankees team doctor Chris Ahmad on Tuesday.
Yankees manager Aaron Boone told reporters on July 31 that Kahnle had been placed on the 10-day injured list after an MRI revealed an injury in his right ulnar collateral ligament.
Kahnle's only appearance this season came in New York's third game. He allowed one hit and one walk and garnered three strikeouts in one inning of the Yankees' 3-2 victory over the Washington Nationals on July 26.
Heyman noted that typical Tommy John recovery time for relievers can range from nine to 12 months. That time frame could put Kahnle's return anywhere from May to August 2021. Next season will be the right-hander's final year of arbitration before he can become a free agent.
The Yankees' relief corps is still in a great position to succeed without Kahnle. The group has great depth with Adam Ottavino, Chad Green, Zack Britton and David Hale already pitching well. Aroldis Chapman, who has yet to appear in a game, received clearance last week to return after being diagnosed with COVID-19 on July 11.
Kahnle was expected to play a large role in New York's bullpen this season before his injury. The 30-year-old had a 3.67 ERA with 45 hits allowed and 88 strikeouts in 61.1 innings last year.