Dr. James Andrews is scheduled to perform an ulnar collateral reconstruction on Smyly's left elbow on July 6 in Birmingham, Ala., according to Mariners general manager Jerry Dipoto.
Typical recovery time from a UCL reconstruction surgery is 12 to 15 months, meaning Smyly is likely to miss most or all of the 2018 season as well.
Smyly, 27, will do his rehabilitation work closer to his offseason home in Dallas.
Smyly was placed on the 10-day disabled list April 2 (retroactive to March 30) with a left arm flexor strain after he appeared in three Cactus League games with Seattle this spring, going 1-0 with a 5.00 ERA. He also made one appearance with Team USA, striking out eight in 4 2/3 innings while allowing just one unearned run on March 15 vs. Team Venezuela. He was transferred to the 60-day disabled list on April 4.
Smyly established career-highs last season with 30 starts, 175 1/3 innings and 167 strikeouts. He finished the season 7-12 with a 4.88 ERA over 175 1/3 innings with 167 strikeouts in 30 starts with the Tampa Bay Rays. Among left-handed pitchers last season, Smyly ranked seventh in fewest walks-per-9.0-innings with a mark of 2.52.
Over his final 12 starts of the 2016 season, Smyly was 5-1 with a 3.73 ERA after opening the year 2-11 with a 5.64 ERA in his first 18 starts.
In five Major League seasons with the Detroit Tigers (2012-14) and Tampa Bay (2014-16), Smyly is 31-27 with a 3.74 ERA over 570 1/3 innings with 552 strikeouts in 156 games (85 starts).
Smyly was originally selected by Detroit in the second round of the 2010 draft. He was traded to Tampa Bay on July 31, 2014. The Mariners acquired Smyly from the Rays in a January trade.