The 22-year-old Brazilian winger faced off with home supporters and pointed directly to one after racist insults during the second half.
Real Madrid goalkeeper Thibaut Courtois said he heard monkey chants near the start of the game, while Los Blancos coach Carlo Ancelotti said there was "a racist atmosphere" at Mestalla.
"It was not the first time, not the second and not the third. Racism is normal in La Liga. The competition thinks it's normal, the (Spanish) Federation also thinks it's normal and opponents encourage it," Vinicius wrote on Instagram on Sunday.
"The league that once belonged to Ronaldinho, Ronaldo, Cristiano (Ronaldo) and (Leo) Messi, now belongs to racists.
"A beautiful nation, which welcomed me and which I love, but one which has agreed to export the image of a racist country to the world.
"I'm sorry for the Spaniards who don't agree, but today, in Brazil, Spain is known as a country of racists. Unfortunately, for everything that happens every week, I have no way of defending it. I agree."
Vinicius Jr says racism is "normal" in La Liga after crowd chants during Real Madrid's match in Valencia 🇪🇸 pic.twitter.com/WrptDZ4Els— Sky Sports News (@SkySportsNews) May 21, 2023
The Spanish top flight said they have been "proactive in the face of all racist incidents" involving Vinicius who was sent off in Sunday's game.
La Liga said they were investigating what happened at Mestalla and will take the appropriate legal action if a hate crime is detected.
"La Liga has filed complaints (to relevant authorities) on nine occasions in the last two seasons," said the top flight in a statement.
"La Liga has been fighting against this kind of behaviour for years and promoting the positive values of sport, not only on the pitch but also off it."
The Brazilian football federation (CBF) president Ednaldo Rodrigues also criticised the incident.
"How long are we going to experience, in the middle of the 21st century, episodes like the one we just witnessed, once again, in La Liga?" he wrote in a statement released by the CBF on Instagram.
Racist Abuse to Vinicius Jr once again, and another time in La Liga— 𝙇𝙞𝙖𝙢🇧🇪 (@OfficialVizeh) May 21, 2023
Effigys, Racist Banners and Chants
Valencia, Mallorca, Atleti, Barca and Valladolid
Mario Balotelli had racism follow him throughout his entire career too, and many others. Tragic man
"How long will humanity remain just a spectator and an accomplice in cruel acts of racism?"
Rodrigues offered the Madrid forward a message of support.
"There is no joy where there is racism," he added.
"You have all our affection and that of all Brazilians, Vinicius."