Bradley said that his teammates are prepared for the clash and completely unfazed by their opponents, despite acknowledging the talent of Ronaldo.
"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 told reporters.
"We understand what a special player [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."
A win over Portugal would secure USA's place in the second round.