The Real Madrid superstar has been plagued with persistent leg injuries, which resulted in the winger missing the Seleccao's 1-0 friendly victory over Mexico on Friday.
Portugal have just nine days to go before they face Joachim Low’s Germany side in Salvador on June 16.
But, Bento has refused to state whether Ronaldo, who is suffering from tendonitis and a thigh problem, will be fit in time to play in the side’s Group G opener.
"The situation is evolving and our expectations are evolving constantly," Bento told reporters.
"When he's ready to play is a decision that will be made just like any other player, regardless of who it is. I'm not at liberty to discuss at full length the situation. As soon as he is ready to train, we will make that announcement.
"We have to prepare for Germany regardless. The decision of if he will play and when is up to me, the player and the doctors. Ronaldo is not the only good player we have.
"But it's also true I can't change your [the media's] opinions. We'll continue with the work we've been developing until now. The only issue is when he will be able to join us and to play."
Ronaldo is not Bento's only injury concern, with defender Pepe and midfielder Raul Meireles also missing out of the Mexico win with leg and thigh injuries respectively.