[9] With several first-team players unavailable through injury or suspension, Cooper was named among the substitutes for the EFL Championship match at home to Preston North End on 1 January 2019, but remained unused.
[4] Cooper signed a one-year professional contract in June 2019,[5] and made his senior debut as a starter in the EFL Trophy against Manchester United U21 in August.
[14] Player-manager and defensive partner Mike Williamson highlighted how Cooper "fitted perfectly into a back three, [and] has been very consistent", rating him a Championship player in the making.
[24][25] He had an eventful game against Kettering Town on 6 November: attempting to head the ball back to his goalkeeper after 8 minutes, he placed it over him for an own goal, gave his side the lead after 64, also with a header, and was fouled for a late penalty, converted by Will Hatfield to complete a 3–1 win.
[27] The loan was extended to the end of the season, and he made 12 appearances (11 starts) and scored once, in a 5–0 defeat of Weymouth,[2] showing himself to be "solid and reliable defensively, and comfortable bringing the ball forward".