Davis and Williams were suspended without pay and will miss Washington's remaining four games.
NFL Network insider Jason La Canfora reported Sunday that Davis and Williams were two of 11 players who tested positive on drug tests after the NFL lockout during the offseason. Citing a source with knowledge of the situation, La Canfora reported the drug levels found in Williams and Davis continued to escalate at times of testing. The other nine players are facing only fines.
Davis and Williams repeatedly tested positive after their first positive test for marijuana in August, a league source told La Canfora on Tuesday, and have been placed in Stage 3A of the league's drug program, which means another positive result would make them subject to a one-year suspension.
Williams had traces of the drug in his system on upwards of 10 tests between August and October, according to the source.
There were ongoing negotiations between the NFL and NFL Players Association about this situation -- as many players incorrectly believed that drug testing wouldn't begin quickly after the lockout ended.
The news comes at a bad time for Davis, who's in the midst of a breakthrough season and headed to free agency as one of the top tight ends on the market. With tight end Chris Cooley on season-ending injured reserve, Davis had a career-high 59 receptions for 796 yards and three touchdowns through 12 games.
Williams, the Redskins' first-round pick in the 2010 draft, started 10 games at left tackle this season. But there were concerns about Williams' motivation and off-the-field activities coming out of college, and to that end, the Redskins structured his contract, with $6 million tied to him reporting on time and being a part of the team's offseason program.
Williams has a $1 million reporting bonus in 2012, $1 million in 2013, $1.75 million in 2014 and $2 million in 2015, as well as $250,000 in salary reductions tied to workout participation in 2011.
Williams is scheduled to make $11 million in salary in 2012 and count $14 million against the cap.
The Associated Press contributed to this report.