Red Sox's Carson Smith needs Tommy John surgery

Boston Red Sox reliever Carson Smith will undergo Tommy John surgery, the club announced Tuesday, a significant blow for a team that gave up an established starting pitcher for Smith's services.

Smith, 26, was one of the American League's best relievers in 2015, when he posted a 2.31 ERA and a 1.01 WHIP in 70 games for the Seattle Mariners. The Red Sox acquired him in exchange for left-handed starter Wade Miley, envisioning a daunting end-of-game combination of Smith, Koji Uehara and closer Craig Kimbrel.

But Smith developed flexor tendinitis in spring training and returned to pitch in three games before the diagnosis of an ulnar collateral ligament tear in his throwing elbow. That will likely sideline him for most of 2017, as well.

The Red Sox have gotten on well without him, as Kimbrel has saved 12 games and Junichi Tazawa has stepped into a higher-leverage role, posting a 1.53 ERA and has eight holds with no blown saves. Still, Smith's loss will be felt as the season goes on, and 2017 comes into view.

GALLERY: TOMMY JOHN RECIPIENTS IN 2016