Former three-time world player of the year Ronaldo said Wednesday that it was too early to make a decision on his future in football.
The Brazilian suffered a ruptured tendon in his knee a month ago and faces at least nine months on the sidelines.
At 31 and with his weight and fitness having been called into question over the last few years, many doubt they will ever see Ronaldo running around a football pitch again.
Ronaldo himself, now recovering in Milan, told the club's TV channel that he could not be sure he would come back but that the possibility was keeping him motivated.
"For now it's too early to talk about a decision, but I'm ready for this big challenge which is returning to play," he said. "I'm feeling better, the worst is behind me. I don't have any more pain and now I'm even managing to walk better.
"There's little time left now before I can remove the cast."
Ronaldo suffered the same injury on his other knee in 1999 and missed the best part of 20 months of action. A similar outcome with this injury would almost certainly end his career.
Without him Milan were eliminated from the Champions League, a competition he has never won, by Arsenal and sit down in fifth place in Serie A.