Ronaldo has side-stepped talk of possible transfers to Manchester City or Flamengo as he continues his recovery from a serious knee injury.
The 31-year-old striker, who is a free agent after his contract with AC Milan expired in June, ruptured knee ligaments earlier this year and has been undergoing rehabilitation in his native Brazil.
He was treated by Flamengo club doctor Jose Luiz Runco, but when asked if he would play for the Rio de Janeiro giants, Ronaldo said: "That will only be decided in the future. At the moment I am only thinking about returning to playing football."
"I would not go through with all this treatment if I was not sure about my return. Football is my passion."
The 2002 World Cup winner revealed he had been approached over a possible deal to join with compatriot Robinho at City next year.
"There was some contact [with City]," he said. "I have some projects but I am focused on getting over this injury."
Although he is expected to return to training in two or three months' time, Ronaldo is refusing to set a date for a comeback.
"I have no date fixed," he said. "We have plenty of time to schedule that."
Meanwhile, Flamengo doctor Runco added that Ronaldo needs to lose weight before he can think about returning to training.
Runco told Radio Brasil: "The player is upbeat. Clinically he is doing very well. He needs to lose weight, then he will start practising with a ball again."
Ronaldo has played down Runco's concerns over his weight, however.
"I haven't played in six months - of course I'm overweight. Everybody would gain weight in a situation like this," he said.