[3] He joined Wigan Athletic at the age of ten in 2013, progressing through the youth teams before being offered a scholarship deal in 2017.

[4] He made his professional debut for Wigan Athletic on 14 August 2018, appearing as a substitute against Rotherham United in the first round of the EFL Cup.

[10] On 11 December 2021, Gelhardt scored his first goal for Leeds in a 2–3 away league defeat to rivals Chelsea[11] and he netted his second on 13 March 2022: a dramatic added-time 2–1 winner at Elland Road against Norwich City.

[12] In the 2022–23 season, Gelhardt's 10 appearances through the end of October were mostly limited to late substitutions, mostly for Sinisterra and Rodrigo,[13] allowing little time for him to impress himself on the direction of the game.

[17] He made his full debut on 21 January scoring Hull's goal in the 2–1 home defeat by Queens Park Rangers.

[23] In April 2019, Gelhardt was included in the England U17 squad for the 2019 UEFA European Under-17 Championships and scored in a 3–1 victory over Sweden under-17s as the Young Lions bowed out of the competition at the group stage.