According to ESPN.com's John Keim, Washington head coach Jay Gruden confirmed Smith broke his tibia and fibula.
Patrick Mahomes was Smith's understudy during his rookie season with the Kansas City Chiefs in 2017. Mahomes showed his support for his former teammate on Twitter.
Smith's injury leaves Washington down to one active quarterback. Colt McCoy went 6-of-12 for 54 yards and a touchdown in place of Smith on Sunday.
Washington has a short week ahead of its Week 12 matchup with the Dallas Cowboys, though. The two teams play in the second of the NFL's three Thanksgiving Day games.