TEMPE, Ariz. -- Arizona State quarterback Steven Threet had decided to walk away from football after suffering four concussions in five years, including two this past fall.

Threet says he had concussions on Oct. 23 at California and another Nov. 26 against UCLA that ended his junior year.

He told The Arizona Republic on Wednesday that he's still experiencing symptoms from the last concussion, including headaches and trouble sleeping. Threet also suffered concussions his senior year at Adrian (Mich.) High School and in 2008 while playing at Michigan.

Threet beat out Brock Osweiler and Samson Szakacsy in a tight battle for the starting job that started in spring that lasted until just before the season started. As a junior, he threw for 2,534 yards and 18 touchdowns with 16 interceptions, and was sacked 23 times.

Threet says he's on schedule to graduate in May.

His decision likely means Osweiler will be the starting quarterback entering spring practice. He threw for 797 yards and five touchdowns and no interceptions in six games and started the season finale against Arizona, leading the Sun Devils to a 30-29 overtime win in Tucson.

Arizona State also will be thin on experience at quarterback after Szakacsy decided to leave the program.