Responding to Real Madrid’s reported interest in Garnacho, De Gea jokingly said: “We won’t let him go”.
De Gea’s response comes after a report from Spain recently detailed that Madrid have earmarked Garnacho for purchase.
The La Liga champions view the Argentine as someone who aligns with their transfer strategy of signing young players destined for the biggest stage.
De Gea played in the opening 45 minutes of the defeat to Real Betis while Garnacho featured for all 90 minutes.
The pair will be expected to play important roles for United when the Premier League resumes with a clash with Nottingham Forest.