Crean was born in Medway, Kent and grew up in Rochester. He played his junior rugby at Medway RFC, starting from the age of five and playing through to the U16s side, and also represented the Kent county rugby team at U15s and 16s level. He then secured a scholarship to attend Harrow School, after being spotted at a rugby festival by Saracens academy coach Rory Teague. His peers at the school included fellow future Saracens academy graduates Andy Christie, Elliott Obatoyinbo, Sean Reffell and Manu Vunipola.[2]
Over the next two years, Crean was dual-registered with both Saracens and Ampthill, with the majority of his matches played for the latter club in the RFU Championship.[3] Subsequently, he was promoted into the Saracens first-team squad on a full-time basis, ahead of the beginning of the 2022–23 season.[4]