Can Rafael Nadal repeat his 2017 success in the upcoming season?

It was a scintillating comeback for the "King of Clay" in 2017. After enduring an injury-plagued 2016, he defied all odds and ended a two-year wait for his 15th Grand Slam title.

But the Spaniard didn't stop there. He reached as many as three Slam finals and ended up adding a 3rd US Open title to his historic 10th French Open trophy.

Ending the year as World No. 1 for the fourth time in his career, it was a dream season for the left-hander in more ways than one.

The only knock on Nadal's season was the resurrection of his arch-rival Roger Federer, who beat him four out of four times - including the five-set thriller in the Australian Open final.

Federer, who won the Australian Open and also Wimbledon, narrowed the head-to-head record to 23-15 and finished second in the ATP rankings for 2017. Nadal will need to find a solution to beat his old nemesis if he wants to dominate like he was doing when the rivalry began.

Given his age, the Spaniard will need to play a lot closer to the baseline against the Swiss master, whose backhand doesn't seem vulnerable to Nadal's lofty topspin forehand anymore. He needs to add a bit more pace to his second serve too, because Federer has been teeing off on that shot.

Grass is another area of concern for Nadal. He needs to tweak his strategy and come to the net more often in order to finish points faster.

Nadal last reached the Wimbledon final in 2011; since then he has been eliminated before the quarterfinals every time. He probably has very few attempts left to increase his Grand Slam tally on the green lawns.

Nadal's withdrawal from both the lead-up events to the Australian Open - the Abu Dhabi exhibition and the Brisbane Open - due to injury concerns won't do his chances any favours. Most observers are skeptical about whether he will be able to compete at the highest level in 2018.

A serial winner, Rafa celebrates being awarded the ATP No. 1 trophy in 2017

Moreover, the comebacks of Novak Djokovic and Andy Murray will be intriguing to watch; they will likely be hungrier than ever to prove their mettle. Djokovic, a six-time Australian Open winner, will be one of the favourites to win the title in 2018 despite not having played for the last six months.

Stan 'the Man' Wawrinka will also begin the 2018 season after an injury layoff, and he will look to use arguably the best backhand in the game to create some damage. And with Alexander Zverev, Dominic Thiem and Nick Kyrgios on the upswing, it will be a treat to watch which players among the young blood carry the baton forward from the Big 4.

All of these factors will make Nadal's job that much tougher, notwithstanding the fact that he's been playing some sublime tennis of late.

The world's No. 1 male tennis player likely has a couple of years left in him, as he confessed in an interview that he doesn't expect to play until the age of 36. Also, his health and fitness will be an issue as he is no longer as fit as he was in his 20s.

If Nadal wants to cling on to the top spot, he will have to play his best tennis throughout the season as he has the most points to defend. Only time will tell whether he will be able to replicate his 2017 success again in 2018.

One thing is almost certain though; whether he's ranked No. 1 or lower, he will continue being a contender at every event he plays. It has always been hard to stop the 16-time Slam champion, and it will likely always be that way.