Cornwell was the first player to commit to first-year Nevada coach Jay Norvell last December and he entered fall training camp as the starter.
But Cornwell didn't make his debut for the Wolf Pack (0-4) until Saturday's 45-7 loss at Washington State.
Nevada spokesman Chad Hartley confirmed in a statement that Cornwell has left the team and asked for his release from the program. Hartley says the school appreciates his contributions and wishes him the best moving forward.
Quarterback Ty Gangi, who started Nevada's first two games, has been named the starter for Saturday's Mountain West opener at Fresno State.