Back-up Washington Redskins quarterback Kirk Cousins suffered a sprained foot in his side's 24-13 pre-season win over the Pittsburgh Steelers last night.

Cousins had been standing in for first-choice quarterback Robert Griffin III, who is currently in a race to be fit for the opening match of the regular season after suffering a serious knee injury in the last campaign.

Cousins picked up the injury while running the ball and being tackled by Steelers linebacker Lawrence Timmons. He returned to the huddle before undergoing some treatment and eventually leaving the pitch.

"I felt it initially, and as I was walking back to the huddle, I started to self-evaluate about could I change directions if needed and be an athlete," Cousins told reporters after the game.

"I started feeling it and decided, 'You know what? Pre-season game number two with a long season ahead of us, now is not the time to try to be a hero'."

With Cousins and Griffin sidelined, the Redskins will turn to third-choice quarterback Rex Grossman, who could start their opening game of the season against the Philadelphia Eagles on September 9.