During an injury-plagued spell that ran from November to March, Rafael Nadal withdrew from six successive tournaments. According to the doom-mongers, his future as a grand slam contender stood in doubt.

Yet over the past six weeks, Nadal has proved that he is not just the king of clay but the king of comebacks, too. Once Nadal's feet had touched the red dirt in Monte Carlo, he began a winning streak that has continued all the way to Roland Garros - with the exception of a single reverse at the hands of Dominic Thiem in Madrid. His unbroken run of 50 straight sets on clay set a world record.

All of which begs two intriguing questions. Is Nadal playing better than ever? Or is the competition weaker than before?

A little bit of both, according to leading tennis statisticians Graeme Spence, Stephanie Kovalchik and Machar Reid from Melbourne-based Game Insight Group.

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According to Elo ratings (which are different to the ATP's rankings because they focus on who you are playing, not where or when), Nadal faced a lower standard of opponent in 2017 and 2018 than he had in previous seasons.

Much of this comes down to injuries and form slumps among the sport's established stars, especially the "Big Four". Nadal hasn't played Andy Murray for 25 months, and faced Novak Djokovic only once last year - the lowest seasonal incidence of this high-frequency rivalry since 2006.

Admittedly, the great Nadal-Roger Federer feud enjoyed a revival. There were four meetings in 2017, all of which Federer won. But none was on clay, as Federer has effectively retired from that surface.

Turning to Nadal's performances, the hiring of coach Carlos Moya - a former world No1 - at the end of 2016 proved to be a masterstroke.

Moya recognised Nadal's power and intensity allowed him to dominate most opponents once the rally had started but that he was less effective than many of his peers on the two most pivotal shots: the serve and the return.

Moya encouraged his old friend, not a gambler by nature, to take more risks with his serve. Analysis of data from clay-court matches shows only how the body serve - once the safe option Nadal used more often than not - has receded so dramatically, he now hits it only one time in 10.

Meanwhile, the most difficult and penetrative serve - the one which flies down the T - has become his favourite this season.

And what of the return? Nadal has always stood a long way back when receiving, but under Moya's guidance, he has moved even closer to the line judges. By the time the ball reaches him, it has slowed down to the point where he can take a full-blooded swing, imparting his usual heavy topspin.

Players serving to Nadal have almost a second longer to prepare for their second shot, because the ball travels perhaps 10m further in either direction. Even so, dealing with his deep, dipping, kicking return is still nightmarishly difficult.

ATP analyst Craig O'Shannessy has recommended bold experimentation as the best response.

"Rafa backs up so far when he's receiving serve, he's halfway to Moscow," O'Shannessy said this week. "So an underarm serve? Why not? I'm not advocating a player continually doing it, but you need an agent of disruption. Perhaps a slow serve-and-volley, more drop shots. Do something radical."

The challenge is all the greater because Nadal is an outlier, tactically speaking, whose game has little in common with anyone else's. The only satisfactory way to prepare for facing Nadal is ... by facing Nadal.

Historically, the figures show Nadal's clay court dominance has grown through his career, with the exception of a hiatus in 2015 and 2016.

Yet there is one chink of light for the rest of the field. Under pressure in Madrid against Thiem, Nadal reverted to old patterns on his serve (more conservative) and return (less depth) in a 7-5 6-3 defeat.

Nadal's search for an 11th Roland Garros title starts against familiar foe Alexandr Dolgopolov, who he has beaten seven times in nine matches. The pair have met only three times on clay, though, with Nadal victorious on all occasions.

•In the women's draw, the return to grand slam action of Serena Williams is sure to dominate the headlines.

The 23-time winner is competing in her first major since giving birth to her daughter in September. She hasn't played a major since winning the Australian Open in January 2017. She is set to face two-time winner Garbine Muguruza from Spain in the quarter-finals.

Nadal at French Open
Years played: 13
Titles: 10
Win/Loss: 79/2
Prizemoney: US$16,912,255