He was unable to train for a fortnight and only got back on to the clay in the middle of last week.
"Now it's time to see how good it is," said the 10-time Grand Slam winner.
"I need to be able to play at my top level and 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 had to travel 60km to Grasse on Sunday to find an indoor court amid heavy downpours, a day after arriving in Monte Carlo.
The 25-year-old said he had his fingers crossed as he prepares to attack an event where his only loss came as a teenager in 2003.
"I hope I can now train without impediments," he said before directing further criticism at the ATP's preference for hardcourt events.
"Clay means less damage for the knees and the body. The worst surface for player health is hardcourt. We are wrong to play more and more on hard and less and less on clay and grass."
The king of clay, whose last trophy came at the 2011 French Open, played down the fact that his last successcame 10 months ago.
"I haven't won a title, but how many finals have I played?" asked Nadal, who has appeared in four finals since his Roland Garros triumph.
"If I played more on clay, like in South America or after Wimbledon, I would have better chances of winning titles.
"There are players there [at lower-profile events] who can beat you, but the chances are better. But I don't make my calendar to win titles, I want to compete at the most important events against the best players ...
"I'm not playing only on my best surface, but to try and win titles. That makes it more difficult. But I don't feel pressure just because I haven't won since Roland Garros."
- AAP
