Ronaldo, who drew a blank in Portugal's opening 4-0 defeat to Germany, has been nursing a troublesome knee problem and has been applying ice to the injury.
It was even claimed in some reports that Ronaldo will be putting his career in jeopardy if he plays against United States in Manuas on June 22, when a defeat for Portugal could send them out of the competition.
But Mourinho says Ronaldo is fit and he sees no reason why his former player at Real Madrid should not take to the field.
"Of course," said Mourinho when asked by Yahoo if Ronaldo should play. "He says he has no problems. The reports in the press... some doctor has denied already making any comments.
"The doctor we have to listen to is the doctor of the Portuguese national team who says that Ronaldo is in great condition.
"The fact that today people are commenting that after the training session he was leaving the session with some ice on his knee - I think that this is more than natural because you always have a little knock here, a little knock there and it is normal that after the recovering session you have some.
"I really don't understand why Portugal today, they had a training session in front of 10,000 people. In my office I was watching the training session live, which is something I don't understand.
"And because of that, everybody could see around the world that Ronaldo was having ice on his knee, but I think there is no problem.
"He played for 90 minutes (against Germany) so absolutely no problem and the doctor from the Portuguese national team is saying that he is in perfect condition and I really believe he is."
- Sports & Recreation
- Cristiano Ronaldo
- Jose Mourinho