"I don't know when we will be able to use him. That's what I said last Friday. When there is something different to what I said before, we will say so," Bento said.
Ronaldo has yet to take part in a full training session with his team-mates since joining the Portugal camp one week ago and also missed last Saturday's friendly with Greece.
What appeared to be a mere case of fatigue following the Champions League final has gradually taken on more serious overtones, with the media now wondering whether he will face the opening World Cup match against Germany.
Midfielder Raul Meireles and central defender Pepe will also sit out the match in Boston. The trio stayed at the Portuguese team hotel just outside New York on Thursday rather than travelling with the team.
Bento clearly became frustrated about the number of questions he had to field about Ronaldo's condition.
"When they are ready to compete, we'll announce it straight away," he said. "Until then, rather than just feeling sorry about their absence or wondering about when they will be 100 per cent, we have to find solutions that allow us to compete as best as possible."
"Ronaldo is not the only one who is injured. We have other players with physical problems and my expectations and opinion have not changed in relation to last week.
"Every absence limits our work. We want to have everyone available but it hasn't been possible and we have to find solutions to try and get around these difficulties and look to the strengths of the players who are available."
Ronaldo is suffering from an injury to his left thigh as well as patellar tendinosis, Meireles has an injury to his left thigh and Pepe a muscle injury in his right leg.
"They will maintain the programme pre-established by the medical department for their injuries, with specific work in the hotel and some sporting interludes on the pitch," said the FPF's daily medical bulletin.
Ronaldo, 29, struggled with minor injuries during the closing weeks of Real Madrid's season before playing 120 minutes in the Champions League final against Atletico Madrid and scoring the final goal in their 4-1 win with a penalty.
Portugal's opening World Cup match is against Germany in Salvador on June 16 and they also face United States and Ghana in their group.
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- Raul Meireles