Halliday, the nation's passing leader, said Thursday that he broke his tibia and fibula when a USC player fell on his leg early in the Nov. 1 game. He says the break was closer to his ankle than his knee.
Coach Mike Leach had told the media that Halliday's ankle was broken.
Halliday said doctors predict he will be running in three months and should be fully recovered in about five months. He plans to try out for the National Football League, which has long been his dream.
Freshman Luke Falk has filled in for Halliday, and will lead the Cougars in this Saturday's game at No. 13 Arizona State.
In nine games this season, Halliday completed 67 percent of his passes for 3,873 yards, with 32 touchdowns and 11 interceptions. He threw for an NCAA record 734 yards in a loss to California, and was on pace to set other national records when he was injured.
Halliday said he and Falk have been teammates for two years, and that he is pleased by Falk's stellar performance in relief.
"It's such a cool feeling to see a guy you feel you helped along the way play so well," Halliday said.
Halliday said he expects to be ready to work out for NFL teams in the spring.
"I will do everything I can to make this a reality," he said.
He is grateful for the support he has received from Washington State fans.
"It means the world to me that people take time out of their day to say a couple of kind words to me," Halliday said. "It shows how strong Cougar Nation really is."
Halliday put up some astonishing numbers in Leach's Air Raid offense, including an NCAA record 89 pass attempts against Oregon last year. He expected Falk will break some of those records.
But the perpetually rebuilding Cougars never had a winning record with Halliday at the helm, and he expects his passing stats to be his legacy.
"It shows I was an explosive quarterback," Halliday said. "When we got rolling there was not too much other people could do to stop it."
Halliday said he knew as he was being tackled that he would likely break his leg. He was twisting away from the tackler, a position he had been in many times in his career. His brain was telling him to move his foot, but he could not because the foot was trapped.
"I heard it happen," he said of the break.
The break is not too painful now, except when he rehabs.
"There's nothing I can do about it now," he said. "I've got to get ready to hopefully have a career at the next level."