The complaint forced the Spaniard to withdraw from his last match against Andy Murray a fortnight ago.
Despite only having a few days to recover, Nadal is confident that he has done enough preparation ahead of his round two match against Finland's Jarkko Nieminen on Wednesday.
"Now it's time to see how good it is," said the 25-year-old. "I need to be able to play at top level, run without thinking about the knee.
"I've put all the effort in and hopefully it is well and I can train in the right conditions. That's the most important thing for me today."
Nadal was victorious in Monte Carlo last year.