As he was given a yellow card for his celebration, the Brazilian claimed he had been racially abused during the Champions League clash against Benfica as play was stopped for 10 minutes.
Alexander-Arnold was asked about the incident after the game on Amazon Prime and replied: “I think what's happened tonight is a disgrace to football. It's overshadowed the performance, especially after such an amazing goal.
"Vini's been subjected to this a few times throughout his career and for it to happen tonight and ruin the night for us as a team is a disgrace. Like I said, it's a disgrace to football. There's no place for it in football or society. It's disgusting.
"It's upsetting. We as people, we come here to do a job, we enjoy what we do. When something like that happens, it takes the fun out of the game and ruins the night for all of us. We stick together as a team, we dug deep and got the win. Most of all, I think we're all proud of the way we handled it."
In a statement in Portuguese on Instagram, shared by Benfica on social media, Prestianni denied making racist comments.
He wrote: "I want to clarify that at no time did I direct racist insults to Vini Jr, who regrettably misunderstood what he thought he heard.
"I was never racist with anyone and I regret the threats I received from Real Madrid players."
The incident will be investigated as officials attempt to work out what was said during the exchange in what is an ongoing story.