Benfica have continued to stand by Prestianni, with president Rui Costa hitting out at the decision to ban the 20-year-old from the second leg.
He said: "I wasn't on the field to know what was said or not said; in a situation like that, a lot can be said. We believe our player's word, who is being labelled a racist, but he is anything but racist.
"We always defended the player, we always kept the player informed of everything we were doing, and I'm only speaking now because there was a decision, even if not final and even if unfair, in our perspective. It wasn't justified for the president to speak before the process was finalised. In the end, there was no sentence, there's only a suspension, but there was no point in talking about a matter that was still in process."
Prestianni's defence that he used homophobic rather than racist language has been denounced by Real Madrid goalkeeper Thibaut Courtois, who declared: "It's just as serious because they are homophobic insults...I've also seen the images from the Benfica stand during the match and I think it's deplorable to see that in a stadium.
"You may like a player more or less, but making those gestures is shameful...I haven't seen if they've said anything about going after their fans who made those monkey gestures.
"But with everything that has happened, there are many things that haven't been done well. I think that racism, homophobia - all of these things - we simply cannot accept them and the insult is equally serious."