Bradley, the Red Sox's No. 5 prospect, singled to start the game and took a turn around second after Jeremy Hazelbaker's one-out single. He appeared to slip or roll his left ankle on the play and went down near second base.
Sea Dogs athletic trainer Brandon Henry and manager Kevin Boles eventually helped Bradley to his feet, and he was able to walk off the field with assistance. The game was delayed about 22 minutes after Bradley's injury as the Rock Cats grounds crew repaired the infield.
Zach Gentile replaced Bradley at second and in left field, with Peter Hissey moving from left to center.
Bradley has been enjoying a solid campaign at two levels -- he's batting .316 with nine homers, 62 RBIs, 24 steals and a .426 on-base percentage between Class A Advanced Salem and Portland.
The South Carolina product was a 2012 Carolina League All-Star after hitting .359 in 67 games before his promotion. With Portland, the 22-year-old has batted .276 in 56 games. He's currently ranked as Boston's No. 2 outfield prospect behind Bryce Brentz.