Ronaldo has been limited to 70 minutes in each of Brazil's first two World Cup matches, but he now feels fit enough to play a full game.
Ronaldo, who trained as usual on Monday afternoon despite banging his head against a low ceiling during a game of table tennis, had appeared frustrated when he was substituted in Saturday's 4-0 win over China.
The second half substitution cost him the chance to add to his 2002 tally of two goals against a vulnerable Chinese defence.
"My physical condition is evolving very well, I could have played longer in the last game but he (coach Luiz Felipe Scolari) preferred otherwise. I was substituted but it was good in some ways," Ronaldo said.
"Maybe in the next game I can stay on for the whole game." Brazil play Costa Rica in their final group C game on Thursday. Ronaldo has not played the whole 90 minutes of an international since returning from injury.
The striker was at pains to point out the team came above his personal ambition of finishing as top scorer at the tournament.
"It's good to make things clear about the idea of being leading scorer," he said.
"I will do everything I can to score goals but the main objective is to be champion."
"I've scored goals all my life and I'm going to continue scoring them but, without doubt, the objective is to win the World Cup and, of course, if I continue scoring goals I will help to them to get there."
He was sidelined for over two years as he underwent two knee operations and was then plagued by a series of muscular problems.
He has said he wants to finish as the World Cup's top scorer to silence those who doubted he would ever be the same player again.