Daniels was on crutches when he came back to the sideline in the third quarter, and he wore a large brace on his right knee, which was wrapped. X-rays came back negative, and head coach Clay Helton said Daniels would undergo an MRI late Saturday.
"Gut-wrenching," Helton said of seeing Daniels go down. "You see a kid who has poured so much into the game and into this team and into becoming better, both physically and mentally, as a quarterback. I said a prayer as soon as I saw it, and I'm hoping we get the best results tomorrow. We'll see where it lies."
Daniels was replaced by true freshman Kedon Slovis, a four-star recruit from Arizona who took over to begin the second half with USC holding a 17-10 lead.
Daniels completed 25 of 34 passes for 215 yards and a touchdown before leaving the game. It was his first start running new offensive coordinator Graham Harrell's system.
Slovis went 6-of-8 for 57 yards and an interception.