Ronaldo, who has suffered tendinosis around the knee, gave a thumbs up to RPT television when asked if he was 100 percent physically and said "it's fine."
Around 10,000 fans watched the open training session in Campinas in a carnival atmosphere.
At one point, a woman ran onto the pitch to try and reach Ronaldo, evaded one security guard and ran another 40 metres before being brought down by another.
Ronaldo, who played in Portugal's 5-1 friendly win over Ireland on Wednesday, went over to sign his autograph on her shirt before the Portugal players threw shirts into the crowd amid hysterical scenes.
Team-mate Joao Moutinho also moved to quell the injury fears.
"Ever since he started to train with us he has been 100% like the rest of us," he said. "Everything is fine with him but there is some caution, not only with him. Many other players were using ice as well. There is nothing to worry about. The ice is normal after training.
Left back Fabio Coentrao was the only player to appear on the Portuguese federation's daily medical bulletin after he missed training because of a bruised right buttock.
Portugal get their campaign underway against Germany in Group G on Monday.
- Sports & Recreation