Cornely has been optioned to Triple-A Pawtucket.
Cornely, 26, made his major league debut on April 29, allowing four runs in one inning against the Washington Nationals. The right-hander has spent the majority of this season pitching for Atlanta's Triple-A affiliate, the Gwinnett Braves, posting a 4.42 ERA and striking out 24 batters in 18 1/3 innings pitched.
"We like the fastball ability," Red Sox manager John Farrell said. "It might not be a pure velocity, but there's some swing and miss throughout the course of his career. Those guys always jump out to us."
Cornely has averaged 12.1 strikeouts per nine innings pitched in his five-year minor league career.