The Champions League play-off first leg clash was suspended for 11 minutes after Vinicius accused Prestianni of using the slur after Vinicius scored for Real five minutes into the second half.
Prestianni denied the allegation, saying Vinicius "misunderstood what he thinks he heard", and Benfica said they stood by their winger as UEFA appointed an Ethics and Disciplinary Inspector to investigate the allegation.
"Real Madrid C.F. announces that today it has provided UEFA with all available evidence regarding the incidents that occurred on Tuesday," Real said in a statement.
The Spanish club said they appreciate the support Vinicius has received since the incident.
"Real Madrid will continue to work, in collaboration with all institutions, to eradicate racism, violence and hatred in sport and in society," the club added.
Benfica will visit Real for the second leg of the tie next Wednesday.