Bulldogs coach Jeff Tedford said the team does not fear the injury will end Haener's season.
During the Bulldogs' first drive of the second half, Haener was sacked by USC defensive lineman Solomon Byrd. Haener lost the ball, which Byrd recovered, and appeared to have his right leg and ankle caught underneath multiple defenders. Haener stayed down -- clearly in pain -- before being carted off the field. He later returned to the sideline on crutches and wearing a boot on his right foot.
Haener, who exercised his final year of eligibility to return to Fresno State for his senior season, had completed 10 of 18 passes for 117 yards with a touchdown and an interception before exiting the game.
The Trojans went on to win 45-17.
Earlier this week, Haener -- who started his college career at Washington before transferring to Fresno State as a sophomore -- talked about how much he was looking forward to playing USC as the underdog, noting that he grew up wanting to play for the Trojans after growing up in Northern California.
"I wanted that offer, but little Jake Haener wasn't tall enough and didn't have enough stars next to his name," Haener said earlier this week. "Now I get the chance to play there."
On the Bulldogs' first drive after Haener's exit, backup quarterback Logan Fife was able to lead Fresno State down the field for a six-play touchdown drive.