Ronaldo says he plans to make his comeback from a career-threatening knee injury in two to three months, possibly with Manchester City.
The 31-year-old Brazilian striker said in the French sports daily L'Equipe on Friday that he faces a "difficult challenge" but his knee is doing "marvelously well" following surgery in February.
"I'm suffering but I'm making progress," he said.
The three-time FIFA player of the year ruptured a tendon in his left knee in an Italian league match in February. He has been without a club since his contract with AC Milan expired in June.
"In two or three months time, I think I will be back into competition," said Ronaldo, who is using Flamengo's facilities in Rio de Janeiro to complete his recovery.
He claimed there is a "great possibility" he will join English Premier League side Manchester City, which is now flush with cash following a takeover by an Abu Dhabi-based company.
Brazilian forward Robinho joined City from Real Madrid for a British record 32.5 million pounds (US$58.6 million) last month.
"We are having discussions," Ronaldo said. "We'll see."
City confirmed this week it had spoken to Ronaldo and his representatives but would not be looking to sign the player.
Ronaldo was photographed visibly overweight while vacationing in Ibiza recently. In April, he made the headlines after being involved in a controversy with cross-dressing prostitutes in Rio.
Ronaldo has battled serious injuries throughout his career, including a right knee injury that kept him sidelined for nearly a year in 2000. He recovered in time to lead Brazil to the 2002 World Cup title, scoring two goals in the final against Germany.