Manchester United manager Erik ten Hag revealed he was unhappy with Alejandro Garnacho in the early weeks of the season.
Garnacho, 18, made his full debut in United's 3-0 Europa League win over FC Sheriff on Thursday night, having appeared against Brighton, Real Sociedad and Sheriff in Moldova.
The Argentine emerged for his United debut against Chelsea in April and he was included in Ten Hag's pre-season tour squad of Australia and Thailand but did not appear in any of the four games.