An MRI revealed the senior quarterback has two cracked transverse processes in his back. The two transverse processes of each vertebrae function as the site of attachment for muscles and ligaments as well as the point of articulation of the ribs (in the thoracic spine).
The injury is not expected to be serious and should heal on its own.
Petty played through the injury in the first half of Baylor's 45-0 win over SMU on Sunday night, then sat out the second half. He finished with 161 passing yards and three total touchdowns.
After the game, Petty said he expects to play on Saturday against Northwestern State.
Former Baylor tight end Jordan Najvar suffered the same injury last season and missed one game, while linebacker Brody Trahan also had the same injury in 2012 and did not miss any games.