Murphy went down against the Ravens during the Redskins' first preseason game, Thursday night. Murphy will miss the rest of the 2017 season.
While Miami's front office and coaching staff will look to move forward without the rookie linebacker, the Redskins were already expecting Murphy to miss the first four games of the 2017 season.
Murphy is coming off his best season as a professional, collecting nine sacks in 2016.
ESPN.com's Adam Schefter reported that Murphy also tore his MCL.
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.
The Redskins are already thin at outside linebacker, where Ryan Kerrigan and Preston Smith are now listed atop the team's depth chart.
He suffered the season-ending injury in the first quarter of Washington's 23-3 loss to Baltimore at M&T Bank Stadium.
A former college star will be out for the upcoming National Football League season. Preston Smith is the team's starter at outside linebacker, with Lynden Trail likely to see more playing time with Murphy out for the season.