Courtois refused to be drawn on comments from Benfica president Rui Costa, who said Prestianni “is not racist” and deserves the club’s trust after “being crucified”, but reiterated his support for his own team-mate.
“Vini has never said anything like that, so I’m 100% sure he heard it,” said the Belgian.
“I believe him completely. Since he’s keeping quiet, we’ll never know for sure, but there’s not much more we can do.”
The tie was halted for 10 minutes after Vinicius alerted referee Francois Letexier to the incident, before his team-mates temporarily left the pitch.
Courtois said Real were prepared to “stand their ground”, but agreed to complete the game after Vinicius said he wanted to continue.
There were also reports of racist gestures in the stands at Estadio da Luz.
“The other things that happened in the stands, in my opinion, warrant stopping the match and kicking those people out,” added Courtois.
“As footballers, we don’t see everything, but it happens when we’re focused on the game. There have to be people in charge who see that.
“There’s a Benfica security guard who’s two metres away and he has to act. We can keep improving in these areas… and stop being so foolish.”
Uefa has subsequently sanctioned Prestianni, 20, on a provisional basis, pending the result of a full investigation by an ethics and disciplinary inspector.
The European governing body said further punishment could be handed out once that investigation is completed.
Real manager Alvaro Arbeloa urged Uefa to use this incident as a chance to make a statement.
“We have a great opportunity to mark a turning point in the fight against racism,” he said.
“Uefa, which has always been and has led this fight against racism, now has the chance not to leave it at just a slogan, at just a nice banner before matches, and I hope that they seize this opportunity.”
