General manager Buddy Nix told the team's website Wednesday that the injury is not season-ending, but Anderson will miss significant time. Nix said Anderson is visiting specialist James Andrews to determine the severity of the injury.
Anderson had difficulty putting any weight on his left leg after being hurt in the second half of a 45-3 loss at San Francisco on Sunday.
The Bills attempted to improve their defense by signing Anderson and Mario Williams in March. The plan's been unsuccessful so far.
Buffalo (2-3), which plays at Arizona (4-1) on Sunday, has allowed a combined 97 points and 1,201 yards in its past two games.