Portugal striker Helder Postiga is not fretting over the fitness of captain and talisman Cristiano Ronaldo ahead of their Group F clash with the United States in Manaus on Sunday.

The reigning World Footballer of the Year was a peripheral figure in Portugal's 4-0 thrashing at the hands of Germany in their opening fixture as he continues to nurse a long-standing knee injury which originally threatened to rule him out of the group stages.

With defender Pepe a certainty to miss the game against the United States through suspension and Fabio Coentrao's World Cup ended by a thigh injury, it remains to be seen if they will be joined on the sidelines by Ronaldo - but Postiga believes there is no concern as to whether the Real Madrid forward will be involved.

"I don't think that (whether Ronaldo will play) is a question to be raised at the moment because he's training with us," said Postiga.

"He is practising with us and he's doing all the exercises. I personally think that the Cristiano Ronaldo talk is a bit too much and I can't imagine how he must be feeling about that.

"But regarding his physical condition, he's been training at his maximum and if it's not listed in the clinical information of our football federation it is because he's fit to play."

Following John Brooks' late winner against Ghana, the Unites States go into the game knowing that a second victory would put them on the brink of qualifying for the knockout stages and push Portugal closer to the exit door.

But Jurgen Klinsmann also has injury concerns ahead of the game, with Sunderland striker Jozy Altidore definitely ruled out with a hamstring problem picked up in the Ghana match.

AZ Alkmaar striker Aron Johannsson and Chris Wondolowski of San Jose Earthquakes are competing to replace the stricken Altidore, although the latter admits filling the boots of a man with 23 international goals is not an easy task.

"Jozy is a special player," Wondolowski said.

"It's like saying 'Hey, go and be Cristiano Ronaldo,' you can't necessarily replace certain aspects of it (Altidore's game).

"But I think both Aron and I bring different styles, different sets of skills that I think are useful, and I think that's what we're going do."

Klinsmann will be hoping whoever gets the nod to replace Altidore will play their part in a second win, meaning he will lead his side into their final group game against his home country of Germany knowing qualification is within reach.