Dareus was seen in the locker room with crutches and his ankle wrapped heavily, according to the Buffalo News. He reportedly suffered the injury Wednesday.
The Associated Press reports the Bills are awaiting test results to find out how serious the injury is.
The No. 3 overall pick has looked as good as advertised thus far, with two sacks in the preseason. Buffalo has a lot of injuries right now; three of their starting linebackers missed practice Wednesday and two of their top three receivers are hurt.
Losing Dareus for an extended period would be a huge setback for the rebuilt defense.