"I haven't decided yet what I should do but I'm ready for anything," the three-times World Player of the Year told a news conference before leaving the Pitie-Salpetriere hospital in Paris.
"I have the will to carry on playing, this is what my heart is telling me to do. But my body is giving me signs that it is tiring and needs rest," he added, speaking in Portuguese and Italian, with Milan sports director Leonardo translating.
"I know that physically and mentally it will be very hard. If at the end of the day, I have recovered and can play again, fine. If not, it will be a very hard decision to make but it will have to be the decision."
Ronaldo, the all-time leading scorer in World Cup finals with 15 goals, ruptured his left knee tendon playing for Milan in a 1-1 Serie A draw against Livorno on February 13.
SIX-MONTH WAIT
The surgeon who operated on the 31-year-old, Eric Rolland, said he would "not be able to run before up to five months and not be able to train before nine months.
"Anything can happen in the next three months because surgery is not an exact science. It will all depend on the rehabilitation.
"We'll have a first check-up in three months and another in six months. From a medical point of view, we'll stay cautious for six months," he added.
"The recovery will not depend on Ronaldo for the first six months. It will all depend on him afterwards. Psychologically, he is a remarkable man."
Ronaldo sustained two serious injuries to his right knee while playing for Inter Milan in 1999 and 2000 but recovered to help Brazil win the 2002 World Cup, scoring both goals in their 2-0 win over Germany in the final.
He went on to play for Real Madrid before joining AC Milan in January 2007.
He hardly featured this season because of a series of injuries and the Champions League holders have yet to commit to a new contract.
"The club will always be by his side," Leonardo said.
Ronaldo played down the issue, saying: "I don't think it's the right time to talk about a new contract. I'm sorry that things have worked out like this."
(Reporting by Bertrand Boucey, writing by Jean-Paul Couret; editing by Trevor Huggins)
