it is true that brazil is the only country in the world to have qualified for the fifa world cup every time the tournament occured, and won the esteemed trophy a record 5-times - this does not mean that all brazilians or cariocas are good at soccer, or that everybody idolizes pelé and ronaldinho - to assume otherwise might create an awkward situation and come of as someone with limited and supeficial knowledge of the country or its people. 

those who are sincere in their own passion for soccer, or happen to know a thing or two about the local teams in rio, can potentially use this as a great way to connect with local fans - there is no harm in casual chitchat, as long as you are careful about which team you endorse.