According to the organization, Robert Renan was the victim of several racist insults on social networks, after having "responded sportingly" to provocations from supporters during the game, played at the Diego Armando Maradona stadium.
The CBF guarantees that the profiles of the authors of the insults are identified and will be sent to the local authorities and to FIFA, with requests for sanctions.
Renan was sent off with a red card just before halftime in the game with Tunisia, which Brazil won 4-1, and when he left the pitch he was the target of whistles from some spectators, mostly from Argentina.
The Brazilian responded to the whistles, showing the CBF symbol and raising five fingers, in an allusion to the number of World Cups of the Brazilian team, Argentina's rival.
In the under-20 World Cup, Argentine fans have shown their support for all teams playing against Brazil.