Benn, serving as a blocker on a kickoff drill during Tuesday's practice session with the New England Patriots, is the third Philadelphia veteran to suffer a year-ending knee injury in coach Chip Kelly's first season, joining receiver Jeremy Maclin and linebacker Jason Phillips.
Benn was acquired from the Tampa Bay Buccaneers in March in exchange for draft picks. In his fourth season out of Illinois, Benn has 862 yards receiving and five touchdowns in his career.
The Eagles also released wide receiver Dave Ball on a day that they opened a week full of practices with New England. On Friday night, the two teams will meet at Lincoln Financial Field in the preseason opener.