Brunell was injured while being sacked by the Giants' Nick Greisen on third down of the Redskins' opening series of the third quarter, and was replaced by former starter Patrick Ramsey. Brunell's status for next Sunday's regular-season finale at Philadelphia is up in the air until the team gets the results from the MRI.
"We'll have to see how it develops in the days ahead," said Coach Joe Gibbs on the Redskins' Web site.
In a comeback season, Brunell, 35, has started all but one of Washington's games, has thrown for 2,909 yards, a career-high 22 touchdowns and nine interceptions.
Washington can clinch a playoff berth with a win over the Eagles. A Redskins' victory coupled with a Giants' loss at Oakland will give Washington the NFC East title.