The Real Madrid forward left his team's session an hour before it ended on Wednesday, sparking fresh fears over his fitness in the wake of a 4-0 defeat by Germany
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Ronaldo was a slight doubt for his country's World Cup opener against Germany on Monday but played the full 90 minutes as his side were hammered 4-0 in Salvador.
Bento now hopes that his captain will be fit for what has become a crunch Group G clash with USA on Sunday.
Portugal's all-time leading scorer could now be a doubt, however, after spending the final 60 minutes of his team's session at Ponte Preta’s Estadio Moises Lucarelli in Sao Paulo with an ice-pack pressed to his knee.
He has regularly trained apart from the group in order not to further aggravate his knee problems and Portugal fans will hope that the decision to end training early was merely a precautionary measure.