Last season, Bell attempted only 16 passes, and five of them game in a 69-13 rout of hapless Florida A&M.
Knight passed for 2,092 yards with 27 touchdowns and only three interceptions — and recorded 943 yards and 15 scores on the ground — during his senior season at San Antonio's Ronald Reagan High School.
He had originally committed to Texas A&M in the spring of 2011, but switched his commitment to OU before his senior year of high school.
Knight spent the 2012 season redshirting at Oklahoma and was named as one of the Sooners' Scout Team Players of the Year.
The quarterback battle began in the spring between Bell, Knight and sophomore Kendal Thompson.
Thompson was considered a viable option until suffering a foot injury on the first day of the Sooners' preseason fall camp this month.