The Brazilian and the Spanish star will be very familiar with each other, having faced off many times as players for Real Madrid and Barcelona.
Real Madrid got the better of Barcelona in their four meetings last season, though a resounding win for the Blaugrana in league play helped pave the way for a La Liga title.
And Casemiro, preparing for Brazil's last-16 World Cup clash against Mexico in Samara Monday, pointed to rival midfielder Busquets when quizzed on who the best in the world at his position was.
"There are not many players that I can choose from in my position but if I had to pick one then it would be Busquets," Casemiro told a news conference Friday.
"He is the best in the world and I have a lot of admiration for him, he has a lot of quality.
"[France duo N'Golo] Kante and [Paul] Pogba are also very strong."
Should Casemiro and Busquets face off in Russia it would be in the final, with the Brazilian possibly having to go through Kante, Pogba and France in the semi-finals to get there.