The Brazilian winger pushed goalkeeper Stole Dimitrievski in the back of the neck amid a spat between the two players and was dismissed.
Vinicius was mocked by Valencia fans at their Mestalla stadium during the game, having squared off with some who racially abused him in a match in 2022.
"I think it is difficult (to be Vinicius), I'm not in his skin, but I think it's difficult," Ancelotti told reporters, after Vinicius saw red in Madrid's 2-1 La Liga win on Friday.
"To bear everything that has happened, the insults, everything, it's not so simple.
"Obviously he's sad about the red card, he said sorry and we have to look forwards."
Vinicius, who has suffered racial abuse at numerous stadiums in Spain, is also often targeted by fans for his behaviour on the pitch.
The 24-year-old often complains to officials after clashing with defenders and sometimes engages and responds to fans who jeer him.
"What happens in stadiums... I think he has improved his attitude a lot, he can keep improving but nobody is perfect," continued Ancelotti.
"I think he's done a lot of work on that, and he has improved so much that he is the best player in the world."
Vinicius may face a ban after his red card, which will be decided next week, meaning he is available for Madrid's Copa del Rey clash against Deportivo Minera on Monday.
"We're still convinced it was not worth a red card but a yellow, so we hope he is not banned," said Ancelotti.
League leaders and reigning champions Madrid then face Mallorca in the Spanish Super Cup semi-final on Thursday in Saudi Arabia.
