Vikings quarterback Christian Ponder suffered a concussion on the next play after taking a hard hit.
Neither player will return.
Putting no weight on his leg, Peterson was helped off the field after taking a helmet-to-knee hit from Redskins safety DeJon Gomes on the first play from scrimmage in the third quarter.
He was playing in just his second game after missing the previous three with a high ankle sprain. Peterson rushed for 38 yards and a touchdown before leaving.