The 18 year-old was asked about the reaction of Vini Jr's teammates to the Brazilian's strop and also the apology that came at the next training session at Valdebebas.
Mastantuono recalled to Cadena SER: “His actions were obviously not the right choice.
"Vinicius apologised to Xabi Alonso and everyone else. The most important thing is that everyone stays united.
"Vinicius is an incredible person. He is often criticised, but he always brings joy to the dressing room. Of course, he gets angry, like all of us. Obviously, the way he left wasn't right.
"He recognised that and knows he's important to the team. He's one of the captains. These things happen in football.”
