Ronaldo was injured in Sunday's 0-0 draw at Real Mallorca and club medical staff believe he will be missing for three weeks.
"I will try to reduce delays. I am working hard for it," said Ronaldo, who is working six hours a day at the Real gym.
Among those driving Ronaldo on is Kaka, who is also recovering from groin surgery. Ronaldo wants to be back on September 15 for the Champions League clash with Ajax.