Murphy is entering his fourth season with the Redskins after being the team's top pick in the 2014 NFL Draft out of Stanford. He suffered the season-ending injury in the first quarter of Washington's 23-3 loss to Baltimore at MT Bank Stadium.
"It's too bad," coach Jay Gruden said of Murphy before practice Saturday. "He was really having a great offseason, then he followed it up with a really good training camp so far. It's unfortunate, you know, just wrong place at the wrong time."
Murphy was slated to miss the first four games of the season after being suspended for violating the NFL policy on performance-enhancing substances.
The 26-year-old Murphy was coming off a career-high 9.5 sacks. In his first three seasons in Washington, Murphy appeared in 47 regular-season games with 22 starts, registering 112 tackles along with 15 sacks, six forced fumbles and four fumbles recovered.
The Redskins also signed free agent wide receiver Jamari Staples on Saturday and waived rookie offensive tackle Kevin Bowen, designated as injured.
Staples, 22, split his college career between UAB and Louisville. He played two seasons with UAB, recording 40 receptions for 648 yards and five touchdowns.
Following the 2014 season, Staples transferred to Louisville after it was announced that UAB's football program was being shut down. In two seasons with the Cardinals, he had 73 receptions for 1,253 yards and five touchdowns.