He finished the season with completing 13 out of 27 passing attempts for 181 yards, two interceptions and two touchdowns and was awarded a redshirt along with an extra year of eligibility.
[6] He was named the Sun Belt Offensive Player of the Week after his performance against Coastal Carolina where he completed 18 out of 24 passing attempts for 198 yards and two touchdowns.
[11] During the 2023 season, Grainger was named the Sun Belt Offensive Player of the Week after his performance during the Week 3 game against Charlotte where he completed 27 out of 33 passing attempts for 466 yards and three touchdowns, while also rushing for 23 yards and a touchdown.
[12][13] On May 25, 2024, Grainger signed to play for the Winnipeg Blue Bombers of the Canadian Football League (CFL).
[16] Late in the season, he was re-signed by the Blue Bombers on September 16, 2024, to a practice roster agreement.