Garnacho, 16, mainly featured in Atletico Madrid’s Juvenil B side last season but also appeared for their Under-19s team.
The Spaniard, who can operate up front as well as on both wings, has completed a period of self-isolation after arriving from the Spanish capital and can now begin training with his new team-mates.
McNeill is a 17-year-old striker who has represented England up to Under-16s level and was a prolific goalscorer during his time in Manchester City’s younger age-groups.
The 2020/21 intake of players have enjoyed successful starts to their United scholarships. Isak Hansen, Joe Hugill and Logan Pye have already had the opportunity to face senior opposition in the EFL Trophy, as well as playing for the Under-18s.