 St. Kevin's had previously produced a number of Republic of Ireland internationals, including Liam Brady, Damien Duff, and Jeff Hendrick.At the age of 15, Mandroiu was signed by Premier League outfit Brighton & Hove Albion.In the 2018-19 season, he made 11 league appearances for Simon Rusk's Under-23 side in the Premier League 2 Division 2, contributing towards the team's promotion to the top flight of under-23 football.