Real Madrid coach Julen Lopetegui has explained his management of Vinicius Junior.
The €45m signing from Flamengo has been registered with Castilla this season, instead of being added to Lopetegui's squad.
The coach explained: "He's an emerging talent from Brazil. We will prepare him well to confirm his promise.
"He is a boy with excellent qualities, but he has to adapt to the requirements of Real Madrid and European football. I do not know if he will play in the Champions League.
"He belongs to Real, he has his chances, but I do not know yet. We did not let him go on loan because we want him to train with us to monitor his progress. Training with us is a fantastic experience for him."