Peterson, who leads the team in rushing with 242 yards and three touchdowns, suffered a dislocated shoulder in Monday night's 43-19 loss at New Orleans. Also dealing with ankle and knee injuries, Peterson was limited to six yards on four carries versus the Saints.
The 33-year-old Peterson, in his first season with the Redskins, had his best game in a Week 3 win over Green Bay, rushing for 120 yards and a pair of touchdowns on 19 carries.
Washington has other injury concerns in the backfield and at the skill positions. Running back Chris Thompson, who is second to Peterson with 100 yards rushing, is questionable with a rib injury.
Thompson also is the team's leading receiver with 26 catches for 200 yards and a touchdown.
The Redskins' top three wide receivers also were listed as questionable. Jamison Crowder and Paul Richardson, who each have 13 catches and one score, are battling ankle and shoulder/knee injuries, respectively. Wideout Josh Doctson missed the last game with a heel injury.
Washington coach Jay Gruden said he expected all of the players to be game-time decisions. The same applies to guard Shawn Lauvao, who is doubtful with a calf injury.