Neymar has been criticised for his theatrics in Russia, but the forward has netted twice and provided an assist in four games.
The Paris Saint-Germain star only made his return from injury last month and Willian feels Neymar is only getting better at the showpiece event.
"All of us know how important he [Neymar] is for our team and what his level of quality is," Willian said Wednesday.
"He has been playing better one game after the other as well. Our plan is to continue evolving, improving, until we get to the final if we are fortunate enough.
"He is an excellent player, he can decide a game at any moment in time, we all know that. So I'm also very happy for the way he's been playing."
Lucas Figueiredo / CBF pic.twitter.com/we9C2sxJnQ
— CBF Futebol (@CBF_Futebol) July 4, 2018
Brazil continue their World Cup campaign with a blockbuster quarter-final against Belgium Friday.
That will see Willian come up against Chelsea team-mate Thibaut Courtois and the attacker praised the Belgium goalkeeper.
"I think it's difficult to play against him because he is very good and he is tall. But, at this time we have to do something special to score against him," Willian said.
"We know the quality he has but I think we have to do our all to score against him. That's what we want at this moment.
"We have goalkeepers here, they have quality like him – Alisson, Ederson and Cassio and I think we have goalkeepers with a lot of quality."
Photo Getty Images. Caption: Brazil attackers Willian and Neymar