On Sunday, Rafael Nadal and Novak Djokovic will face key physical and mental tests as the European clay-court season kicks off at the Monte Carlo Masters. For Nadal, it's all about his troublesome left knee. For Djokovic, the major goal will be to emerge from a minor slump which left the world number one short of the quarter-finals at both the Indian Wells and Miami Masters events last month.

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The Serb, embroiled in ATP political issues as president of the Player Council, has admitted to recent distractions. "I just had way too many things off the court. I guess that affected me a little bit on the court," he said after going out in the last 16 in Miami. Djokovic has plenty on the line at his home base in Monaco, with the 31-year-old looking ahead to completing a possible "Djoko Slam" with a French Open title in two months. Djokovic has collected trophies at Wimbledon and the US Open before defeating Nadal last January for the seventh title in Melbourne.

"I grew up on clay, so I like playing on it, though statistically, hard court was always my most successful surface," Djokovic said after exiting in Miami. "I definitely have to play better." The winner of 15 Grand Slam titles admitted that he was not particularly fit for the American hardcourt swing. "I didn't feel my best health-wise, as well, in Indian Wells and Miami. But, hey, look, you learn that's life."

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