Washington State head coach Mike Leach told reporters after the game that Halliday was in surgery, but would not specify what the injury was.
Halliday leads the nation with 3,833 passing yards this season. The senior has completed 67.3 percent of his passes for 32 touchdowns and 10 interceptions. Halliday also set the single-game FBS record for passing yards (734) in an Oct. 4 loss to Cal.
Freshman Luke Falk replaced Halliday in the game. The Cougars are 2-6 (1-4 Pac 12) this season.