He Real Madrid have soccer surplus (27 under contract at the moment) and while the future of those who have to leave is resolved (Foreman and Reguilón) and those that the club would like to draw (Bale and Mariano), the entity use Castilla as a 'bridge' to save chips federation of the first team. So He has done it with Rodrygo and Lunin. Although the Brazilian is listed on the Madrid club's own website as a first-team footballer, both the striker and the Ukrainian goalkeeper who will act as Courtois' substitute now have a record with the subsidiary led by Raúl.
Is a completely legal method that Madrid has been using regularly for several years. In fact, Vinicius upon arrival was registered with Youth A Madridista because his age at the time (18 years) allowed it, saving the club space for the first team even though the forward was for all intents and purposes a Lopetegui player at the time. The same strategy you used last summer with Take Kubo, while his assignment was resolved to a First, finally to Mallorca.
Although it is an essentially administrative resource, Vinicius and Rodrygo did come to get blanked with the subsidiary White. Rodrygo was in fact being used with Castilla when the pandemic broke out and football stopped. Upon returning, the young attacker did so … as a starter with Zidane.
In the case of Lunin, he returns after his two assignments (Valladolid and Oviedo) and as published by AS, winning the game over Areola. His condition is that of substitute goalkeeper and will not play for Raúl in Castilla. That position, the hinge between the two teams, is for the third goalkeeper, Altube.