The discovery was made after a Monday morning MRI showed that bones sticking out from the spine were cracked, according to a spokesman. Petty said he has pain but expects to play this week against Northwestern State. The injury is expected to heal on its own.
The Big 12's 2013 Offensive Player of the Year was hit from behind on his first run Sunday night against SMU early in the first quarter. Petty was visibly gimpy the rest of the half but continued to play. He was removed at halftime. After the game the situation was termed a bruise and "nothing serious."
Before Monday's diagnosis, coach Art Briles was asked why Petty played the rest of the half after seemingly being hurt. Briles echoed the nothing-serious aspect adding, "He needed the reps."
"I'm bummed out because it's never fun being hurt," Petty said. "Bummed out because I just watched tape and everything is off. You never want to make any excuses. When you're throwing and I can't torque [it's frustrating]. Every time I went to throw it would jolt. It felt like somebody was punching me in my side."
Monday was a day off so Petty won't be able to test to the back on the field until Tuesday. Petty said the injury is being treated with ice and other non-invasive methods.
"Right now, [I] can't sit down right, can't walk right," Petty said.
He finished seventh last year in the Heisman voting.
Petty is the second Big 12 quarterback to be hurt in the opening week. Texas' David Ash will miss Saturday's game against BYU with concussion symptoms, the school said.