Thornton, 36, suffered the injury in his last appearance, August 4 at Fenway Park against the Arizona Diamondbacks. Since joining Boston on July 13, he has gone 0-1 with a 2.16 ERA (2 ER/8.1 IP) in 10 games. Overall this season, Thornton is 0-4 with a 3.47 ERA (14 ER/36.1 IP), 12 walks, and 27 strikeouts in 50 games between the Red Sox and Chicago White Sox.
The 26-year-old Beato will rejoin the Red Sox for his fourth major league stint of the year. In his nine games for Boston in 2013, he has gone 1-1 with a 3.12 ERA (3 ER/8.2 IP) and four strikeouts. With Pawtucket, he was 5-3 with three saves, a 2.09 ERA (10 ER/43.0 IP), 18 walks, and 35 strikeouts in 26 games out of the bullpen.