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.