[4] He was named in Linfield's 25 man Champions League squad against Rosenborg BK by manager David Healy.
[5] On 27 July 2020, the Yorkshire Evening Post revealed that Allen had agreed a deal with newly-promoted Premier League side Leeds United.
[6] The move was officially announced on 11 August, with Allen signing a three-year deal.
[8] He signed his first professional contract with Leeds United in December 2020, agreeing a deal lasting until summer 2023.
[11] On 9 August 2024, Allen returned to NIFL Premiership side Linfield on a two-year contract.