Friday’s quarter-final in Kazan should be another World Cup classic.
Brazil and Belgium are ranked two and three in the Fifa rankings – behind only Germany.
Pre-tournament favourites Brazil were held by Switzerland and struggled to overcome Costa Rica in the group stage, but impressed in the second half of their last-16 win against Mexico.
Martinez said: “When you play against Brazil, you have to understand you are playing against the best team in the competition.
“We will have a real clarity of how to play against players like Neymar and Philippe Coutinho, that can change the game in a second.
“As a boy, you dream of playing in the World Cup against Brazil so we have to enjoy it.”
In the other quarter-final in the top half of the draw, Uruguay face France at 15:00 BST on Friday.
Social media reaction
Martinez certainly had the last laugh, as his decision to bring on Chadli and Fellaini when chasing two (or three) goals was widely mocked on Twitter.
The much-maligned Fellaini scored five goals last season for Manchester United while Chadli only played six times in an injury-hit season as West Brom were relegated.