According to NFL Network's Mike Garafolo, Murphy will serve his four game suspension while on Injured Reserve.
He wasn't going to start for Washington, but Murphy would have played a key role as a backup and in the Redskins' nickel package, as he did last season.
Murphy, 26, was second on the Redskins with nine sacks a year ago, trailing only Ryan Kerrigan.
Coming off of a nine sack breakout year in 2016, Murphy would have been suspended the first four games of the 2017 season for violating the NFL's policy on performance-enhancing drugs had he not been injured.
Rookie Ryan Anderson, Lynden Trail and Chris Carter will each see extended playing time in the absence of veterans.
The Redskins are already thin at outside linebacker, where Ryan Kerrigan and Preston Smith are now listed atop the team's depth chart.
"It's too bad", coach Jay Gruden said of Murphy before practice Saturday.
Safety Su'a Cravens also sustained a knee injury in the game, but is considered day to day. He'll miss two to three weeks with what one source described as a "tweaked" knee, something that dates to his days at USC.