The team announced that Smith, who arrived in Boston this offseason via a trade with Seattle, would undergo ulnar collateral ligament reconstruction Tuesday. The procedure was performed by Dr. David Altchek in New York.
"It's unfortunate,'' Red Sox manager John Farrell said. "You see a guy that has extreme talent, but more importantly, you feel for the guy.
"With Tommy John ... that bell rings loud when a pitcher is faced with that. He has a lengthy road ahead of him now, but it's also a clear-cut path. There's clarity to this. And while it's disappointing, there's a road ahead for him that's well-marked out at this point.''
Smith was placed on the 15-day disabled list last week with right elbow soreness. It was his second time this season on the DL after beginning the season sidelined with a strained flexor muscle in his forearm.
The 26-year-old made just three appearances since coming off the DL on May 3, only allowing an unearned run in 2 2/3 innings.
He was expected to be a key component of the Red Sox bullpen after a 2015 campaign with the Mariners in which he had a 2.31 ERA, 13 saves and 92 strikeouts in 70 innings.
Red Sox president Dave Dombrowski wouldn't rule out a potential trade to add depth to the bullpen, but he doesn't anticipate any moves on the immediate horizon.
"You're always concerned about every scenario,'' Dombrowski said. "It's something we'll continue to watch. There's still quite a bit of time between now and the trade deadline. I feel comfortable the way it is now, but we'll continue to wait and see.''
Information from The Associated Press was used in this report.