Vini Jr had a meltdown during Sunday's victory over Barcelona when coach Xabi Alonso moved to take him off for Rodrigo Goes on 71 minutes.
The Brazil attacker was furious with the decision and after shouting and make angry gestures he stormed down the players' race, rather than take a seat in the dugout. Eventually Vini was seen in the home dugout, but was visibly still brooding.
Valdano said on Movistar+: "Vinicius loses control. He's out of control... he seems absolutely uncontrollable, and he even goes to the locker room and doesn't even stay on the bench.
"I don't know if anyone talks to Vinicius in the Real Madrid locker room or not. If they talk to him and convince him, or if Vinicius reconsiders his attitude and returns to the bench in peace. It's his way of saying, 'I got carried away, forgive me'."
Valdano also spoke about the brawl at the end of the Clásico, which featured Vinicius: "What happens is that once the match is over, Vinicius goes off the rails again, this time against Lamine Yamal.
"There's an element of lack of control that's affecting Vinicius."
But on the player's performance, Valdano also said: "Vinicius was playing very well, he had a good match, he felt physically comfortable, he looked very strong, and he didn't understand the change because he was convinced that he had the ability to turn the game even further."