Already reeling from a crushing 4-0 defeat to Germany in their opener, Portugal face almost certain elimination if they lose to US. But their preparation for the game could not be going much worse. (Agencies)
Although the Portugal camp insist the Real Madrid forward is fit, Ronaldo has been seen sporting an ice pack on his knee at training sessions and leaving early as his team-mates continued to train, while he was far from his scintillating best against the Germans.
Much media speculation has focussed on whether or not he will play against the US, or indeed if he does, whether or not he will be fully fit.
But fellow forward Helder Postiga was adamant that too much is being read into an ice pack.
"I personally think that the Cristiano Ronaldo talk is a bit too much so I imagine how he must be feeling about that," Postiga said.
"But regarding his physical condition, he's been training at his maximum and if it's not listed in the clinical information of the Portuguese (football) federation it's because he's fit to play," he said.
But Ronaldo is just one of Portugal's problems as they will be missing several other players.
Real centre-back Pepe has been suspended for one match after his stupid and needless red card against Germany for headbutting Thomas Mueller, who went on to score a hat-trick.
Given his volatile nature, that may be a blessing in disguise in a tournament where one error can prove hugely costly.
Fabio Coentrao has been ruled out of the tournament with a torn thigh muscle while forward Hugo Almeida has a pulled hamstring and reserve goalkeeper Rui Patricio pulled a thigh muscle.
It is hardly the ideal preparation to face buoyant USA, who began their campaign with a last-gasp 2-1 win over Ghana, avenging defeats to the Black Stars at the last two World Cups.
Yet Portugal coach Paulo Bento believes that his side are simply better than their opponents.
"The best version of Portugal can beat the United States. We respect the USA as a very good team," he said.
"They have grown up over the last years so we have to respect them but we believe in ourselves, we believe in our work, in our quality, so we have to be responsible, we have to be in the best condition to win this match and we believe it."
The US are not without problems of their own as striker Jozy Altidore is out of the game due to a hamstring injury, although US Soccer believe he could be available later on in the tournament.
There is better news when it comes to Clint Dempsey, the opening goalscorer against Ghana who broke his nose in that match. He is likely to line up against Portugal wearing a protective face mask.
Centre-back Matt Besler, who like Altidore had to come off in the first half against Ghana due to a hamstring problem, is another who should be fit to play.
Already reeling from a crushing 4-0 defeat to Germany in their opener, Portugal face almost certain elimination if they lose to US. But their preparation for the game could not be going much worse.