The 2012 Offensive Rookie of the Year, who won the Heisman a year earlier while at Baylor, tweeted on Wednesday, "they doubted in high school, they doubted a turnaround at Baylor, they doubted a Heisman was possible. Keep doubting. It's nothing new."
The 24-year-old, a Pro Bowler in 2012, has been severely limited with his playing time these past two seasons because of knee injuries and surgeries.
The Redskins have won both of their preseason games and play next on Saturday on the road against the Ravens. Washington travels to Houston to play the Texans on Sept. 7 for Week 1 of the regular season.
GALLERY: GRIFFIN-ING AND OTHER TRADEMARK LOOKS, MOVES IN NFL
- Marc Weinreich