Clay king Rafael Nadal has admitted that he is nervous about his Wednesday start at the Monte Carlo Masters, a fortnight after quitting with knee pain prior to his last match.
"I'm scared because this is the start to an important season for me," said the Spaniard, who is bidding for an unprecedented eighth straight title on the clay of the principality. "Hopefully it will work well."
Nadal, seeded second behind Novak Djokovic, will play Finn Jarkko Nieminen in the second round.
In first-round play, Austrian 15th seed Jurgen Melzer beat Lukas Kubot 6-2, 7-5 and Frenchman Paul-Henri Mathieu, ranked 352 after a long absence with a knee injury, crushed Donald Young 6-0, 6-1 to leave the American winless in his last five events.
Australian Bernard Tomic reached the second round by beating Denis Istomin of Uzbekistan 6-4, 6-3.
After quitting before his Miami semi-final against Andy Murray on March 30 due to pain in his left knee, Nadal returned to Spain for injections and treatment of the tendon problem that was causing him grief.
He was unable to train for a fortnight and only got back onto the clay in the middle of last week.
"Now it's time to see how good it is," the 10-time Grand Slam-winner said.
"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 60 kilometres to Grasse on Saturday to find an indoor court amid heavy downpours, a day after arrving in Monte Carlo.
The 25-year-old said that he had his fingers crossed over his physical condition, 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 success came 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.
"It all depends on your calendar. 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 of the world.
"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."