Leinart thus put a lucrative professional career on hold for 12 months. There had been a chance the San Francisco 49ers could have used the No. 1 choice in the 2005 draft to select the USC quarterback.
Leinart won the Heisman Trophy in 2004 and then led the Trojans to a one-sided victory over Oklahoma in the national championship game.
He threw for 3,332 yards and 33 touchdowns last season and could become the second player ever to win the Heisman Trophy twice. Ohio State's Archie Griffin did so in 1974 and 1975.
"I realize there's a small (injury) risk that I'm taking, but it doesn't factor into my head," Leinart said.
"There's something special right now (at USC) that's going on that I didn't want to give up."