BYU spokeswoman Carri Jenkins said Wednesday that Unga, who broke the school rushing record last season as a junior, cannot return to school until winter semester, in January 2011, at the earliest.
That decision was finalized at the end of the school year, Jenkins said, and Unga was informed of the decision at that time.
In April, Unga withdrew from BYU due to a violation of the honor code, along with Keilani Moeaki, who was a member of the women's basketball team and Unga's former fiancee. Moeaki cannot return to school until January 2011, either.
With any chance of playing for the Cougars in 2010 gone, Unga could enter the National Football League supplemental draft this summer.
Meanwhile, BYU will lose not only its leading rusher the past three seasons, but a leader on an offense that is breaking in a new quarterback.