Neymar was left furious after he was sent off under the "Vinícius Júnior rule" on Saturday night.
The Santos star covered his mouth with his hand as he argued with Bahia's Rodrigo Nestor in his side's 1-0 win in Brazil's Serie A.
Nestor alerted the referee who produced a red card for Neymar.
Red cards for players who cover their mouths while talking to opponents were approved for the World Cup, after Real Madrid's Vinícius said he was racially abused by Benfica's Gianluca Prestianni last season in the Champions League. Prestianni was later given a six-game ban for discriminatory conduct that was anti-gay.
Brazil superstar Neymar has now fallen foul of the rule that was brought in for the World Cup.
"We were just chatting in the middle of the field, joking around, laughing with each other," Neymar said.
"Then I went to speak to Nestor -- I was wrong to put my hand over my mouth, sure, but I hadn't even said anything yet when he raised his hand. It's one of the dirtiest tricks in football! But I'll get back at Nestor eventually."
Nestor said: "It was just a standard foul in the course of play. I reached out to shake his hand, and he threw the ball at me. Afterward, he said a number of things to me. I was raised very well by my mother and father. I know exactly where I come from. I was born [in a neighbourhood in São Paulo], it was very difficult to get to where I am today, and I am proud to wear the Bahia jersey.
"He knows what he said to me. It was highly disrespectful -- both toward me and toward the Bahia jersey. While he may be an idol to everyone as a player, today he failed -- he failed miserably as a person -- because of the way he spoke. You shouldn't do things like that.
"I learned a great deal from my mother and father, and I am grateful for the upbringing they gave me. I would never do something like that. I'd rather not repeat what was said, as there are many people watching -- including children. It wasn't right."
Later, Neymar commented on social media: "I'm not one to talk much about what happens during a game -- especially when it's just a back-and-forth between players. I ended up getting sent off, too, and I usually don't dwell on these things, but today, I think it was something very serious. It went beyond the norm, you know?
"I defend this badge -- I'll give my life for it. I'll curse at people, I'll fight, I'll argue -- that's all fine; it stays on the pitch. It's football -- that's just how it is. And sure, he has to defend his side, too.
"But what Nestor did to me today is, in my view, extremely serious. It's serious because there's a law in place against racism, and he tried to gain an advantage in the match by claiming I said something -- even though I had my hand over my mouth and didn't say a word to him. Obviously, we were trading insults -- taking jabs at each other -- and that's fine; it's part of the game. But what he did is very serious.
"We were just messing around -- I was joking with the two centre-backs -- and he used that to try and gain an advantage. That is very serious. There's a law against racism -- how could he do something like this? It's surreal. I'm very sad about what happened, because he was being completely underhanded.
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Neymar accused Nestor of "putting on an act" and warned that the rule to send players off for covering their mouths could cause "underhandedness."