Portugal's Helder Postiga dismissed fears over Cristiano Ronaldo's long-term fitness as the injury-affected star trained for the vital FIFA World Cup™ match against USA.

The captain had his left knee taped as he took part in light drills at the team's training camp near Sao Paulo, raising expectations that he will play in Sunday's game in Manaus.

Some observers have questioned whether the Real Madrid forward was risking aggravating his condition by playing at the FIFA World Cup, but Postiga said Ronaldo was able to train unimpeded.

"I don't think that's a question to be raised at the moment because he's training with us, he's practising with us and he's doing all the exercises," Postiga told reporters. "I'm not a doctor but I don't think that's in question."

Ronaldo, 29, caused further concern over his fitness on Wednesday when he stopped training early and had ice applied to his knee at a public session.

Regarding his physical condition, he's been training at his maximum.

Helder Postiga on Cristiano Ronaldo

Today, though, he showed no signs of discomfort as he took part in a warm-up passing exercise with team-mates Nani, Miguel Veloso, Postiga and Ruben Amorim.

Portugal also have injury concerns over goalkeeper Rui Patricio, striker Hugo Almeida and defender Bruno Alves, who are all undergoing treatment.

But Postiga said Ronaldo had been training "at his maximum" ahead of the game against USA, who beat Ghana 2-1 in their Group G opener.

"I personally think that the Cristiano Ronaldo talk is a bit too much so I imagine how he must be feeling about that," the striker added.

"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."