Both teams have made bright starts to the tournament, which Spain are hosting, winning their opening two matches.
Spain are considered favourites to top Group A and go deep at the event, but this is their biggest challenge yet in Granada.
Wins over Iran and Egypt were expected, but Brazil will test them with the South Americans among those teams capable of having a serious impact.
Pau Gasol (22.5 points per game) and Serge Ibaka (18) have led the way for Spain.
"We want to win every game," Gasol said.
"We want to get better as we go along. We know it's not win-or-go-home at this point, but I think the next three games are three good tests for us to improve and move on to the eighth-finals."
Brazil have been unable to score as freely as Spain, with Leandro Barbosa (9.5 points per game) their leading scorer.
Also in Group A, France should be too good for Egypt and Serbia are likely to overcome Iran.
In Group B, Greece and Croatia are expected to make it three wins from as many games.
Croatia take on Senegal in Seville, Greece meet lowly Puerto Rico and Argentina will fancy their chances against the Philippines.
After their first win at the World Cup since 1998, Senegal are hungry for more.
"We are happy to win our first game at the World Cup," Senegal coach Cheikh Saar said.
"We are very humble and honoured to play in this competition. Nobody expected us to at least win a game except us. We have to be greedy, say we want more and look forward."