He suffered the injury in last Sunday's 16-10 win at New Orleans.
"He didn't take work at all (last week) and I think we took a real hard look at that," Coach Joe Gibbs said Saturday on the team's Web site.
In 48 straight starts for the Redskins, the 6-foot-3 inch, 253-pounder has 220 solo tackles, 14 1/2 sacks, and six forced fumbles.
The seven-year veteran was a second-round draft pick by Indianapolis in 2000, and spent four seasons with the Colts.
To date, he is the Redskins' second-leading tackler (106), and has 2 1/2 sacks, two forced fumbles, and two fumble recoveries.
Sunday's game at St. Louis will be his first absence since he joined the Redskins in 2004.