Washington announced Williams' suspension on Twitter and issued an official statement:
Per Mike Jones of the Washington Post, Williams was suspended for missing a drug test.
This is Williams' second four-game suspension for violating the NFL's substance abuse policy. He previously missed the final four games of the 2011 season for failing "multiple drug tests," according to Jones and colleague Mark Maske.
In May 2012, Williams spoke publicly about his suspension for the first time, telling reporters, "I made a mistake, and I've just got to deal with it."
Per ESPN's Field Yates, Williams' latest suspension will be costly:
Williams has been a rock on the Washington offensive line since the team drafted him fourth overall in 2010. He only missed three games from 2012 through 2015 and was named to the Pro Bowl each of those seasons as well as the All-Pro second team in 2015.
Per Pro Football Focus (via Jeff Dooley of the Washington Post), Williams was ranked as the NFL's seventh-best player regardless of position following Week 7.
Backup left tackle Ty Nsekhe has appeared in all eight of Washington's games so far this season and should slot into the starting role until Williams returns.
Washington does have a bye this week to prepare for life without Williams, though its first test will be significant in Week 10 against the stout Minnesota Vikings defense.