Real Madrid are among the clubs trying to sign Manchester United academy player JJ Gabriel.

Earlier this week, the 15-year-old sent United formal notice that he wants to cancel his registration with immediate effect, but the club can challenge the request.

It is understood a number of major teams across Europe, including Barcelona, Paris St-Germain and Bayern Munich, have a firm interest in the forward, but multiple sources have described Real's efforts to sign him as strong.

The Spanish side want to recruit the teenager immediately and position him in Real Madrid Castilla - the club's recognised reserve team.

Unlike in England, Castilla play in senior football and are in the regionalised third league of the Spanish system. Last season, they were coached by Alvaro Arbeloa, who then took over the senior Real side following Xabi Alonso's dismissal and has since moved to Fulham.

Thiago Pitarch, who was 18 at the start of last season, played for Castilla in a Premier League International Cup match against Southampton in October and made 16 senior appearances during the campaign.

Sources close to Gabriel, who turns 16 on 6 October, feel let down by United, arguing promises around the pathway to the first team have not been kept.

The club say it was anticipated Gabriel would become their youngest senior player by playing in Wednesday night's EFL Cup tie with Brighton. Given they lost 3-2 after leading 2-0, it is debatable whether that would have actually happened.

United have not given up hope of keeping Gabriel, though they are unsure precisely why he wants to leave.

It is understood the player is not currently training with the club.

Speaking after the Brighton game, head coach Michael Carrick, who gave the youngster his senior debut during the pre-season match with Atletico Madrid in Stockholm said everyone needed to be mindful of Gabriel's age.

"I just think we've got to be really careful of the whole situation," he said.

"He's a young boy. He's 15, and for me, definitely, and from a club point of view, looking after our younger players - their welfare, their well-being, their exposure - we've got to be really conscious of that in this situation."

Sources close to Gabriel have dismissed concerns over the player's age and physicality and feel the likes of Max Dowman, who made his debut for Arsenal at the age of 15 last season, show a willingness to trust youth in a way they do not see at United.

Chelsea are also believed to have a major interest in the teenager.

Any imminent move away from Old Trafford for Gabriel is complicated by rules governing the registration of young players.

United say Gabriel's registration runs to the end of the season. It would be easier for him to leave United then, when he will be 16.

However, as Gabriel has an EU passport, he may be allowed to join a club within the European Union on his 16th birthday.