One of the traits of Novak Djokovic's personality that has led him on a track to become the best tennis player on the planet is his refusal to rest on his laurels.

Then again, when there's a hole in his resumé the size of France, he probably finds it easy to strive for more.

Rafael Nadal's Return To Tennis Elite Unlikely

What's interesting is the road block he perceives ahead -- Rafael Nadal.

The current No. 1 player is already being asked about closing that one gap in his career -- winning the French Open to complete his career Grand Slam. Djokovic has 11 majors, but none at Roland Garros.

Djokovic is also already getting some mentions about completing the calendar Grand Slam -- winning the Australian Open, French Open, Wimbledon and U.S. Open in the same year.

As the clay court season approaches, Djokovic will have his second opportunity to hold all four Grand Slam titles simultaneously, according to news.com.au.

Joker entered the 2012 French Open with the chance to become the first man since Rod Laver in 1969 to hold all four major championships. But he lost to Nadal in four sets.

Djokovic finally solved Nadal in 2015, defeating the confidence-shaken Spaniard in the quarterfinals, only to lose to Stan Wawrinka in the finals. But it's Nadal, not Wawrinka, Roger Federer, Andy Murray or any other player, that Novak believes is his main threat in Paris.

"Absolutely," he told via news.com.au. "You would be disrespectful to everything he has achieved in his career on clay courts if we didn't see him this year -- and each year -- as the ultimate challenge on clay courts.

"Everybody knows he is the king of clay. He's achieved so much on that surface. He's made history. He's won the French Open nine times. So, yeah, it's definitely going to be interesting to see how everything unfolds on that surface."

Nadal, currently No. 5 in the world, had talked about his growing confidence in 2016 before bowing out in the first round of the Australian Open. Though Nadal doesn't appear to be the player he was three years ago -- the last time he was No. 1 -- he still beat Djokovic in 2014 in the finals of the French Open.

But if Nadal's confidence fades again, Djokovic will be the overwhelming favorite to win in Paris and complete his career slam.

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