Ronaldo's fitness had been in doubt after struggling with tendinosis in his left knee, and despite training on Sunday with the injured area taped up, the goal machine said his niggles were all in the past.
"I've been practising now for some days and if I'm doing that it is because I am feeling well," Ronaldo told reporters.
"If I am not ready I am the first to tell the coach I don't want to play and I can't play. If I feel anything during the match, which I am sure I won't, I'll be the first to say."
Despite scoring an avalanche of goals in club competitions along with claiming the game's top club titles and trophies, Ronaldo has just two goals in 10 World Cup matches.
One was a penalty against Iran in 2006, and the other the last strike in a 7-0 drubbing of North Korea in 2010.
Asked if a great World Cup was what was lacking in his glittering career, the 29-year-old responded emphatically.
"I don't think I have to show anyone anything. If you look at my statistics and my resume...I have no words for that question," he told a packed news conference.
"I think I do not have to demonstrate anything, not now, before, not after. What I have to do is just continue my career, which has been great so far."
Ronaldo credited the strength and depth of Portugal's opponents Germany ahead of their clash at the Fonte Nova arena in Salvador, but said that respect for the opposition must be ignored once the game starts.
"I am confident we will start off on the right foot," Ronaldo said, before firing a warning that could spell a busy afternoon for Germany's defence.
"I am ready, I am feeling well, and I really want to have a great World Cup."
- Sports & Recreation