Uefa has launched an official investigation after Vinicius, 25, reported alleged racist abuse by Prestianni during Real Madrid's 1-0 win against Benfica in Lisbon on Tuesday.
The Champions League match was halted for 10 minutes by referee Francois Letexier, with both sets of players leaving the pitch shortly after Vinicius had given his side the lead.
The forward, who has been the victim of numerous incidents of racist abuse during his playing career, said in a post on Instagram: "Racists are, above all, cowards. They need to put their shirts in their mouths to show how weak they are.
"But they have the protection of others who, theoretically, have an obligation to punish them. Nothing that happened today is new in my life or in my team's life.
"I received a yellow card for celebrating a goal. I still don't understand why. On the other hand, it was just a poorly executed protocol that served no purpose."
Prestianni, 20, denied directing racial abuse to Vinicius in a post on his social media.
"I want to clarify that at no time did I direct racist insults to Vini Jr, who regrettably misunderstood what he thought he heard," said Prestianni.
"I was never racist with anyone and I regret the threats I received from Real Madrid players."
In a post on their official X account, alongside a video of the alleged incident, Benfica defended Prestianni.
"As the images demonstrate, given the distance, the Real Madrid players could not have heard what they claim to have heard," was the Portuguese club's message.
What did Mourinho say?
Benfica manager Jose Mourinho was seen speaking with Vinicius after the player took the decision to walk off the pitch following the interaction with Prestianni.
The Portuguese said in his post-match interview that he was told different things by Vinicius and Prestianni regarding the incident.
In addition to expressing his belief that Vinicius had been disrespectful with his goal celebration, he pointed to the club's legendary striker Eusebio as proof that Benfica is not a racist club.
Asked if he felt Vinicius incited the crowd, Mourinho said: "Yes. I believe so. It should be the crazy moment of the game, an amazing goal.
"Unfortunately [he was] not just happy to score that astonishing goal. When you score a goal like that, you celebrate in a respectful way."
He added: "I told [Vinicius], when you score a goal like that you just celebrate and walk back. When he was arguing about racism, I told him the biggest person in the history of this club [Eusebio] was black.
"This club, the last thing that it is, is racist. If in his mind there was something in relation to that, this is Benfica.
"[Vinicius and Prestianni] told me different things. But I don't believe in one or another. I want to be an independent."
'Disgrace to football' - the reaction
Real defender Trent Alexander-Arnold said the alleged abuse of his team-mate was a "disgrace to football".
"What has happened is a disgrace to football and overshadowed the performance, as well as an amazing goal," said Alexander-Arnold.
"Vini has been subject to this a few times throughout his career. To ruin a night like this for our team is a disgrace.
"There is no place for it in football or society. It is disgusting."
Former Real Madrid midfielder Clarence Seedorf, working as a pundit for Amazon Prime, said Mourinho "made a big mistake to justify racial abuse".
"I think he is still emotional," said the Dutchman.
"He's saying it's OK, when Vinicius provokes you, to be racist - and I think that is very wrong.
"We should never, ever justify racial abuse. Vinicius has had enough of that unjustified behaviour from people. I know Mourinho by heart would agree with me but he expressed himself a bit unfortunately."
Former England and Arsenal forward Theo Walcott, who was working alongside Seedorf, also condemned Mourinho's comments.
"I am quite calm and composed and I am not someone who gets angry often," said Walcott.
"I love everything Jose Mourinho has done in football but he has made a poor decision. It was maybe the one time we shouldn't have heard from him, the one night he should not have been in front of the cameras."
Former Arsenal and France striker Thierry Henry, speaking on CBS, reflected on his own experiences of racist abuse during his playing career.
"I can relate to what Vinicius Junior is going through. That happened to me so many times on the field. At times you feel lonely because it's going to be your word against his word, because we don't know what he has said," Henry said.
"He put his shirt over his mouth. Clearly, already, he looks suspicious because he didn't want people to see what he said.
"Let's see how big of a man Prestianni is – tell us what you said."
What happens next?
Uefa, which organises the Champions League, launched an investigation into Vinicius' claims on Wednesday.
"A Uefa Ethics and Disciplinary Inspector has been appointed to investigate allegations of discriminatory behaviour," it said in a statement.
"Further information regarding this matter will be made available in due course."
If Prestianni was to be charged and consequently found guilty of using racist language, he would face a minimum 10-match ban from European competition.
This mandatory punishment was introduced in 2013 by Gianni Infantino when he was Uefa general secretary.
It was applied in British football in 2021 after a Europa League game between Slavia Prague and Rangers.
Ondrej Kudela, a centre-back for the Czech club, was found guilty of racially abusing Glen Kamara and received a 10-match suspension.
Vinicius' team-mate Kylian Mbappe called for Argentina winger Prestianni to no longer be allowed to play in the Champions League following the alleged incident.
"Nothing like this has ever happened to me, and in these kinds of important matters, it's important to speak very clearly and not to speak in generalities," France forward Mbappe said.
"I have the utmost respect for Benfica and their coach, who is one of the best in history and who made history with Real Madrid. But, in my opinion, this player doesn't deserve to play in the Champions League any more.
"We cannot accept that a player who plays in Europe's top competition behaves like this.
"Let's leave it to Uefa, who always try to do something. Now they have a serious case, and I hope they do something."