Kyle Beckerman said the United States are preparing to face Portugal captain Cristiano Ronaldo, despite uncertainty surrounding his fitness.
Ronaldo has struggled with knee tendonitis but played in Portugal's 4-0 Group G loss to Germany, though his participation at the FIFA World Cup has been cast into doubt recently after reports claimed he was forced to leave training early on Wednesday.
Portugal team-mate Miguel Veloso played down Ronaldo's injury concerns, insisting the country's all-time leading goal scorer was fine ahead of Sunday's do-or-die clash, with defeat enough to end the Europeans' campaign.
And midfielder Beckerman insists the USA, who defeated Ghana 2-1 in their opening match, will be keeping a close eye on Ronaldo, with victory in Manaus virtually assuring Jurgen Klinsmann's men a spot in the round of 16 - should Germany beat the African nation on Saturday.
"So far it's just been about watching their team," Beckerman told reporters.
"We'll get into tiny details and things like that when it gets a bit closer but we all know it's going to take 11 of us completely focused.
"We're going to have to know exactly where he (Cristiano Ronaldo) is at all times while we're attacking, that's when he can be most dangerous because lose the ball and next thing you know it's in the back of your net.
"That's how dangerous he is. We're going to have to be aware of him at all times and be really clean with the ball.
USA team-mate Jermaine Jones, who has formed a formidable partnership with Beckerman in the centre of midfield, says the chance to seal their progression into the knockout phase with a group game to spare will provide extra motivation for the players.
"We'll do everything and try everything to win this game," Jones said.
"So if we win the game and they lose it we can say that they are out of the tournament so I'm 100 per cent sure that they will try everything to win it.
"We have a lot of respect for the players they have in their team but we know if we win that game, we are already through to the next round so we'll be concentrating 100 per cent on that game."
