Dudek injured himself in a non-contact drill, the Illinois athletic department said in a statement.
The 2014 freshman All-American will have surgery as soon as possible and is projected to return in October, said head coach Tim Beckman.
Dudek had a breakout season for the Illini in 2014, catching 76 passes for 1038 yards and six touchdowns.
Depending on when in October Dudek returns he could miss between four and seven games of the 2015 season.
- Will Green