Mustapha was one of the first names on the team sheet for Darren Powell, featuring in all but one of the U21s’ 30 fixtures in the 2024/25 campaign.
The 18-year-old scored 11 times in 29 games for the U21s, while also registering seven assists. He scored some sensational strikes, including a half-volley against Brighton & Hove Albion and a 25-yard screamer against Chelsea - both of which were nominated for the Goal of the Season.
His strong performances saw him earn a deserved place in the first-team mid-season friendly squad which traveled to Marbella to face Hamarkameratene back in March.