The Red Sox say reliever Tyler Thornburg will have season-ending right shoulder surgery.
Boston says the right-hander will be treated in St. Louis for thoracic outlet syndrome. The condition results from the compression of nerves or blood vessels between the neck and the armpit.
Thornburg has not pitched for Boston since he was acquired in an offseason trade with the Brewers for Travis Shaw.
In five seasons with Milwaukee, Thornburg has a 14-9 record with 13 saves and a 2.87 ERA in 144 career appearances.
He is expected to be ready for the 2018 season.