Vikings' Peterson injured again

Vikings running back Adrian Peterson left Saturday's's game against the Washington Redskins in the third quarter with an apparent injury to his left knee.

Peterson, who was playing in just his second game after missing the previous four with a high ankle sprain, was helped off the field after taking a helmet to the knee from Redskins' safety DeJon Gomes on a three-yard run up the middle.

"He has a sprained knee and were going to evaluate his condition once we get home," Vikings head coach Leslie Frazier said of Peterson's injury.

Peterson had rushed for 38 yards and a touchdown before leaving the game.

Vikings quaterback Christian Ponder also suffered a concussion on the next play after taking a hard hit in the third quarter and will not return to the game. Ponder was 8-of-13 for 68 yards before exiting the game.

"Suffered concussion-like symptoms, so by league rule we had to do some things protocol wise," Frazier said. "He'll be evaluated further once we get home as well."

Peterson was replaced by Toby Gerhart, while Ponder was replaced under center by Joe Webb.