NEW YORK — Yankees left-hander Jordan Montgomery has undergone Tommy John surgery, which will sideline him until the second half of next season or possibly 2020.

Head team physician Dr. Christopher Ahmad operated Thursday at New York-Presbyterian Hospital. The team announced the reconstructive operation repaired a torn ulnar collateral ligament in Montgomery's left elbow, consistent with a recent MRI. A loose bone chip also was removed.

Montgomery, who turns 26 in December, was 2-0 with a 3.62 ERA in six starts after going 9-7 with a 3.88 ERA in 29 starts as a rookie last season. He left a May 1 outing against Houston after one inning because of tightness in his elbow.

Right-hander Domingo German is 0-3 with a 6.33 ERA in five starts since replacing Montgomery in New York's rotation and is 0-4 with a 5.44 ERA in 10 appearances overall. He is scheduled to pitch against Steven Matz (2-4) in Saturday's middle game of a three-game series against the Mets at Citi Field.

Masahiro Tanaka (7-2) starts Friday's opener against Jacob deGrom (4-0), and Luis Severino (9-1) faces Noah Syndergaard (4-1) on Sunday night in a matchup of aces.