Murphy tore the ACL and MCL in his left knee in Thursday's preseason opener vs. Baltimore. Murphy already was going to miss the first four games of the season after being suspended for violating the NFL's policy on performance enhancing drugs.
Murphy, a free agent after the season, was coming off a career-best nine sacks and was playing well in the preseason opener before the injury.
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 was playing behind Ryan Kerrigan and Preston Smith. The Redskins wanted to be creative with their outside linebackers, with both Smith and Murphy capable of playing inside in certain packages -- as they did on occasion in 2016.
The Redskins also have Junior Galette, who has looked sharp in camp after missing two seasons with Achilles injuries, and rookie second-round pick Ryan Anderson. Coaches have been pleased with how he's performed in practice. Veteran Chris Carter, more of a special teams player, also can fill in at outside linebacker. Lynden Trail is another possibility.
The Redskins did catch a break with safety Su'a Cravens, who also underwent an MRI Friday. He'll miss two to three weeks with what one source described as a "tweaked" knee, something that dates to his days at USC.