The Americans made a brilliant start to their Group G campaign in Brazil, scoring inside 29 seconds via Clint Dempsey and firing a late winner to down Ghana 2-1.
The USA can secure qualification to the last 16 with a win over the Portuguese in Manaus on Sunday.
Bradley said for their unfancied side to go up against UEFA Champions League winner and Ballon d'Or holder Ronaldo was worth acknowledging.
"When you play against good teams, when you play against good players, it's important to prepare in the best possible way. I think we've done that," Bradley said.
"We understand what a special player he (Ronaldo) is. We understand how good of a team they have. But it's not something that fazes us.
"We're excited by the challenge. We're excited by the moment.
"We feel like we've put ourselves in a good position, but still everyone is mindful of the fact that it's just one game.
"Now, to follow up a good start to the tournament with another result. That's the only thing we're worried about."
Striker Dempsey said his side would not be focusing on Real Madrid star Ronaldo, who remains under a fitness cloud with a knee issue.
"I think that you have to focus on the team as a whole," Dempsey told FIFA.com, when asked about Ronaldo.
"Yes, there are players who can make a difference and make something out of nothing, but at the same time you have got to focus on the whole team and figure out a way to manage the game and try to put yourself in the best position to get points."
USA coach Jurgen Klinsmann told a news conference he wanted to see his team put Ronaldo and Portugal in their place.
"We want to put Cristiano and his team in place," he said.
"We want to get out there with all the energy that we have, with all the discipline that we're going to bring, with all the aggression we're going to bring to our play and make it our game."
