Smith suffered a subluxation in the shoulder when he threw his glove in the dugout following an outing against the Oakland Athletics on May 14. He was placed on the 10-day disabled list the next day and has been sidelined since.
Red Sox trainer Brad Pearson told reporters Tuesday that Smith also has battled issues with the labrum in the shoulder, which Pearson attributes to the throwing of the glove.
"He had done a really good job with all his rehab up to that point, including making his shoulder strong," Pearson said. "I think it's a freak thing. It's unfortunate that it happened. Who knows where his arm was in space when he was throwing. Sometimes most of the injuries happen on the awkward plays. I would classify this as an awkward motion, and just bad luck."
Smith will miss the remainder of the year after appearing in just 11 games between his first two seasons in Boston due to Tommy John surgery in May 2016 and the subsequent recovery.
Smith, 28, posted a 3.77 ERA with 18 strikeouts in 14 1/3 innings across 18 appearances this season. The Red Sox acquired Smith in a deal with the Seattle Mariners in December 2015.
--Field Level Media