Willian, 25, may replace Neymar for Tuesday's clash against Germany after the Barcelona forward was ruled out for the remainder of the tournament with a broken vertebra.
The Chelsea midfielder was unwilling to accept comparisons to Neymar, who has scored four goals at the World Cup and excelled for the host nation.
"There is nothing to compare with Neymar, or to make comparisons with other players. Neymar is a top player," Willian told a news conference.
"I think that my style is difference from Neymar's. We have a few things in common like speed and dribbling, for example, but Neymar is more a striker and I'm more of an attacking midfielder. I look more for plays.
"Neymar is a player that scores a lot of goals. I'm more a player that helps out the other team-mates. I score some goals, but I'm there more to help.
"We have some similar qualities, and I'm ready and prepared. If Felipao (coach Luiz Felipe Scolari) opts to put me in, I'll go in and do my best."
Willian, who has made 10 appearances for Brazil, said he was ready to start and replace Neymar in the first XI if required.
"I have never started for the Brazil squad, so if I started for the Brazil squad in a semi-final in the World Cup it would be something incredible for me," he said.
"So I'm calm and I'm ready for whatever manager Felipao needs."
