Piland's most recent concussion came on Sept. 7 against Temple.
The junior says: "It was not easy to hear that I can no longer play the game that I love, but I know that our medical staff has my best interests in mind."
Piland ends his career with 5,790 yards passing and 41 touchdowns. He started 10 games last season and finished with 2,929 yards with 16 touchdowns and 12 interceptions. His first season starting for the Cougars came in 2010 when Case Keenum suffered a season-ending injury.
Piland set an NCAA single-game record for most attempts without an interception with 77 last season against Louisiana Tech.