That means he will be out of the rest of the season.
Hobbs was placed on injured reserve Wednesday and will require surgery. Eagles coach Andy Reid says the surgery should allow Hobbs to play again.
The Eagles acquired Hobbs during April's draft, sending a pair of fifth-rounders to the Patriots in exchange for the five-year veteran.
Hobbs recorded 14 tackles in eight games backing up starters Asante Samuel and Sheldon Brown. He also averaged 24.1 yards on 20 kickoff returns with a long of 63.
With Hobbs out, the Eagles said they've signed Ramzee Robinson to play at CB.
Robinson was orginally drafted by the Detroit Lions in 2007 and was released in September, 2009 as part of the team's roster cut down.
He will wear jersey number 28.
The Associated Press contributed to this report