The injury occurred during the Eagles Sunday night practice, though Bradley was able to walk off the field.
Bradley was entering his third NFL season.
Last year for the Eagles, Bradley put up 100 tackles, two sacks, and one interception.
Bradley is not the only Eagle with injury troubles.
Star running back Brian Westbrook is listed as probable, though he will miss most of the preseason due to an injured ankle.
Kevin Curtis, also listed as probable, has returned to practice after a battle with a thigh contusion.
Shawn Andrews is currently questionable due to a tightness in his surgically repaired back after a morning conditioning run on July 31.
In all, the Eagles are battling injuries even before preseason kicks off.
Eagles fans must now hope that everything and everyone will be ready for action come Week 1.