Flu are at home to relegated Guarani at the Enganhao in Rio on the last day of the season on Sunday looking to lift their second national title since 1984.
The 52-year-old man suffered a heart attack during the morning as he stood in line in baking sunshine at Fluminense's headquarters and was pronounced dead on arrival at hospital, the club's health office said.
Other fans also had a bad time in the sun and some gave up after hours of waiting.
"I've had enough, it's clear I'm not going to make it. I spent the night here, I wanted to be absolutely sure (of a ticket), but I'm not okay. We're not clowns to be treated in this way," complained 19-year-old Felipe Dias, speaking to the globoesporte.com website.
Fans had been camping outside the club since Monday night for one of the 45,000 tickets which were only put on sale on Wednesday.
Flu have been playing their home games at the Enganhao, home of city rivals Botafogo, since the giant Maracana stadium was closed for 2014 World Cup refurbishments earlier in the season.
Fluminense are a point ahead of Corinthians, who meet also relegated Goias. Third-placed Cruzeiro are a point further back going into their final match against mid-table Palmeiras.
