The person spoke on the condition of anonymity because the team hasn't released any information or confirmed Dareus was hurt.
The injury occurred in practice Wednesday, during a portion that is closed to reporters. Dareus was briefly spotted walking on crutches in the locker room after practice.
Dareus was drafted third overall out of Alabama in April and is being counted on to make an immediate impact in improving what was a porous Buffalo defense last year.
The Buffalo News first reported that Dareus hurt his left ankle.
Copyright 2011 by The Associated Press