Vinicius was subjected to racial abuse at the Mestalla on Sunday when Real Madrid suffered a 1-0 defeat to Valencia.
The Brazil international was subsequently sent off in the final minutes following a scuffle that saw him hit an opposition player.
Many Black footballers have since leapt to Vinicius’ defense, with Williams also adding his voice to calls for racism in football to be tackled.
“Racism is inadmissible in any circumstance, in football and in society. Let's get this over with. No to racism,” Williams wrote on Twitter.
Meanwhile, Vinicius took to Instagram to slam La Liga and described Spain as a country that has normalised racism.
“It wasn’t the first time or the second or the third. Racism is normal in La Liga. The competition thinks it’s normal, as does the federation, and the opponents encourage it,” the 22-year-old said.
“The championship that once belonged to Ronaldinho, Ronaldo, Cristiano [Ronaldo] and [Lionel] Messi today belongs to the racists.
“A beautiful nation, which welcomed me and which I love but which accepted to export to the world the image of a racist country. I am sorry for those Spaniards who disagree, but today, in Brazil, Spain is known as a country of racists.”
“I am strong and I will go all the way against the racists,” he said. “Even if it is far away from here.”
Vinicius has been backed by Kick it Out and the Professional Footballers Association (PFA) after suffering abuse at the hands of racists.