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

— -- PITTSFORD, N.Y. --? 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 NFL Insider Adam Schefter.

The violation stems from another positive test for marijuana, sources confirmed to Schefter. The positive marijuana test was first reported by NFL Network.

Dareus can appeal the suspension, which would keep him out of the first four games of the regular season. The sixth-year defensive tackle was previously suspended for the first game of the 2015 season for a violation of the substance-abuse policy following a May 2014 arrest in Alabama for criminal possession of a controlled substance.

The suspension is another blow to the Bills' defense, which lost starting outside linebacker Shaq Lawson to offseason shoulder surgery that is expected to keep him out until Week 6 at the earliest, a source told Schefter. Buffalo also will be without starting inside linebacker Reggie Ragland this season after he tore his ACL in training camp.

In the absence of Dareus, the Bills could turn to veterans Kyle Williams or Corbin Bryant to start at nose tackle in Rex Ryan's 3-4 defensive scheme. The team also signed a pair of veteran defensive linemen Monday -- Brandon Deaderick and Alameda Ta'amu -- to add depth.

In addition to Dareus, the team will be without second-year running back Karlos Williams for the first four games of the season for a violation of the NFL's substance-abuse policy. The Bills will be subject to a steep fine from the NFL based on the NFL's remittance policy -- the result of having multiple players suspended in a single season.

Dareus, 26, was named to the Pro Bowl in 2013 and 2014. The third-overall pick of the 2011 draft, Dareus signed a six-year, $100 million extension with the Bills last September.