The Portuguese club, per Sky Sports, have denied reports that Prestianni told his team-mates that he did use a racial slur against Vinicius in the first leg of their tie.
Their statement read: "Sport Lisboa e Benfica categorically denies that the player Prestianni has communicated to the squad or the club's structure that he has uttered a racist insult to the player Vinicius Jr, from Real Madrid.
"As has already been made public, the player apologised to his teammates for the incident that occurred during the match against Real Madrid, regretting the dimension and consequences of it and assuring everyone, as he has done since the first hour, that he is not racist."
Prestianni was seen covering his mouth with his shirt when talking to Vinicius during the first leg last week. The Brazil international quickly alerted referee Francois Letexier, who initiated the anti-racism protocol, prompting a ten-minute delay before the game restarted. Benfica have stood by Prestianni, who has maintained that Vinicius misheard what he said, while manager Jose Mourinho claimed after the match that the Portuguese club could not be racist because club legend Eusebio was black. His comments were widely criticised by figures throughout European football.