The incident happened in the 51st minute of Real Madrid and Benfica’s Champions League round of 16 second leg at the Estadio da Luz.
After Vinicius Jr scored the winner, Benfica players, unhappy with his celebration, confronted the Real Madrid man.
The 25-year-old then told referee Letexier that Prestianni, 20 had racially abused him, and the game was stopped for several minutes.
Speaking to RMC, Letexier, 37, opened up on the difficulty to make a decision in such a volatile environment.
"It’s a very unusual moment. It’s a moment where we don't have all the information," he said.
"We have to decide without having all the facts. In this kind of situations, the most important thing is to gather as much information as possible and, above all, to take precautions. That is my priority."
"When a player comes to tell me that he has been the victim of racist insults that I didn't witness, I have to take what he tells me into account, but I can't make a decision solely on that basis, which seems legitimate to me," Letexier added.
"You have to formalise the situation, make it clear to everyone, and explain to the various parties that the fact that I neither saw nor heard the incident prevents me from taking a disciplinary action. That's how I tried to handle the incident."