Davis will undergo surgery in the next few days and will be out for an undisclosed amount of time.
The 6-foot, 213-pound freshman played only two games last fall as a high school senior at Missouri City, Texas, because of a broken ankle. He missed most of his junior year with a broken collar bone.
"Unfortunately, Knile Davis, we found out - actually late last night when he went down and got x-rays - we found out he had broken the same bone he had broke in high school," Petrino said. "He'll get operated on as quickly as possible. Certainly he is done for spring and we will just have to see how the summer goes on whether he is available for two-a-days or not.
"It is disappointing - real disappointing for him. He was a guy that was doing very well. He is going to be very explosive and very physical and has something a little extra in his heart so I feel real bad for him that that is what it ended up."
Petrino said coaches were optimistic about the injury following Tuesday's drills.
"Yesterday on the practice field they thought it was just a sprained ankle because the soreness and the pain were on the inside," he said, "but when the x-rays came back there was a break in there."