With the Brazilians bidding to become the first South American side to win the title in over a decade, Diniz said he was confident his side can pull off a shock win over the Champions League holders, who he described as "one of the best teams in the history of world football."
"When you go out there to play football, the first thing you have to have is confidence that you can win," Diniz told a press conference in Jeddah, Saudi Arabia.
"I've always gone in with the intention of winning the game. Fluminense will do everything possible to win. We're up against the best team in the world, but that doesn't stop us from dreaming and doing our best.
"What we're going to do tomorrow is be the best we can be."
After being relegated to Brazil's third division in 1998, Fluminense have become a symbol of progressive soccer in the country under the guidance of offensive-minded coach Diniz.
His attractive style of play earned him an offer to take a part-time job as Brazil caretaker while the FA officials allure Real Madrid manager Carlo Ancelotti to accept the position that has been vacant for over a year.
The manager guided his side to their first Copa Libertadores title last month and even received high praise from rival Pep Guardiola, who said Fluminense's style of play was like watching the Brazil of old.
A style that Diniz promises that his side will be faithful to when they face City as a clear underdog, with former Real Madrid full-back Marcelo as their biggest name.
"Fluminense will play like a team that believes in its values and believes that things are possible," Diniz said.
"There's no recipe for us to win. We're going to do what we do best. We're not going to deviate from our characteristics.
"We've prepared a lot. We've been watching them for a long time, we've mapped them out, we've studied them. They're a very complete team, very well-trained.
"We'll try to do our best with a lot of humility, be intelligent in the game and have the courage to do what we usually do."
