Sources: Bills DT Marcell Dareus facing 4-game drug suspension

Buffalo Bills star defensive tackle Marcell Dareus is facing a four-game suspension for another violation of the NFL's substance-abuse policy, league sources told ESPN's Adam Schefter.

Dareus still could appeal the suspension, sources told Schefter. But the injury-plagued Bills are now in danger of losing yet another key defensive player.

Dareus was suspended one game last year for a violation of the league's substance-abuse policy.

The Bills already are without rookie pass rusher Shaq Lawson, who is expected to miss at least the first month of the season after undergoing shoulder surgery, and rookie linebacker Reggie Ragland, who had season-ending knee surgery last week. Bills linebacker IK Enemkpali also will miss the season because of a knee injury.