It's 10 years since the rankings didn't feature either Rafael Nadal or Roger Federer in the top two, but current leading men, Novak Djokovic and Andy Murray, still face a test of clay-court nerve.

On Sunday, Nadal begins his bid for a ninth successive Monte Carlo Masters title.

The 26-year-old Spaniard, who was seven months out of action with a knee injury, has already hammered home his clay-court dominance in 2013 with comeback titles at Sao Paulo and Acapulco.

The seven-time French Open champion romped through the Latin American clay-court swing with a 12-1 record.

His clay record for the past 12 months reads 35-2, although his fitness faces another grueling challenge on European clay this year.

Nadal, currently the world No 5, has a mountain of points to defend after he clinched Monte Carlo, Barcelona, Rome and the French Open in 2012.

His only blip last year was a last-16 defeat to compatriot Fernando Verdasco in Madrid on the hated blue clay which has since been banned.

Nadal is desperate to return to clay on which has won 38 of his 53 career titles.

"I missed the feeling of going onto a big stadium with all the people, all this atmosphere that makes you feel something different," said Nadal, who added the Indian Wells Masters hard-court title to his CV in March.

"And the feeling of victory, the feeling of competition, this adrenaline in life."

Federer, with his 32nd birthday fast approaching, is sitting out Monte Carlo, but his clay-court record - 10 titles on the surface - is 15-2 over the past 12 months.

That puts him second only to Nadal, having captured the Madrid crown in 2012 before succumbing to Djokovic in the semifinals in Rome and Roland Garros.

World No 1 Djokovic, the runner-up to Nadal at Monte Carlo in 2009 and 2012, goes into the tournament confident that a right ankle injury sustained on Davis Cup duty won't limit his chances.

"After seeing the results of all the tests we did, I am really positive and strong," Djokovic wrote on his Facebook page.

"I'm doing the best I can with my team to recover fast and be ready for the upcoming tournaments."

Djokovic's loss to Nadal in the French Open final last year ended his hopes of completing a career Grand Slam.

The Serb failed to lift a clay-court title in 2012 having swept Rome, Madrid and Belgrade 12 months earlier.

Murray remains an enigma on clay.

The US Open and Olympic champion has collected 26 career titles but has never reached a claycourt final, let alone lift a trophy.

Last year, the Scot managed just quarterfinal runs at the French Open, Monte Carlo and Barcelona.

"My consistency has been better over the last few months. The rankings obviously reflect that," said Murray.

"So I will try and keep working hard during the clay (season) and hopefully I can go higher."