Novak Djokovic crashed out of the 2017 Australian Open after an epic 5-set encounter against world number 117 Denis Istomin. After a stunning and record-breaking run of Grand Slam wins throughout 2015 and 2016, at the same time becoming one of a handful of male players achieving a career Grand Slam, Djokovic has now only reached the final in one of the last three Grand Slams, losing to Stan Wawrinka at Flushing Meadow at the end of 2016.

According to Pat Cash, the former Wimbledon winner believes that Djokovic has 'lost his edge' having won everything there is to win in the game.

No longer the player he once was, Cash feels that, with very little left to achieve, Djokovic may not have the desire to compete at the high level that he himself had set.

Whilst naturally Djokovic refutes such talk, stating that anyone can lose a match on any given day, there exist questions on his desire to remain at the top of the game. With Rafa Nadal and Roger Federer both aging and their bodies creaking with injuries under the strains of performing at such exorbitant levels for so long, the path is now Open for Sir Andy Murray to reign supreme at the top of the Men's game for years to come. So Who Are His Challengers?

Milos Raonic

The 26-year-old and current world number three Canadian has been steadily rising up the rankings in the last few years, impressing players and fans alike with his strong serve, quality net play, and calm temperament.

After years of questioning weather, the classic style of serve-and-volley was extinct, watching Raonic play his trade to much success over the years has led many to assert that such a form of the game still has a part to play in the era of back-court and high-fitness Tennis. A two-time Grand Slam semi-finalist and 2016 Wimbledon Finalist, Raonic possesses the skills and qualities to ensure Sir Andy Murray will be looking over his shoulder in 2017.

Kei Nishikori

Already a hero in his native Japan, Kei Nishikori has been impressing many with his never give in attitude and an all-round game that has provided many a scare for the current world leaders. A Grand Slam finalist in 2014, Nishikori's performances have been a little erratic since. Yet as a stalwart at the business end of the ATP Top 10, and finishing 2016 as a semi-finalist at the US Open, 2017 is the year for Nishikori to make his push for World Number 1 and become even more of a hero in the hearts and minds of his Japanese supporters!

Stanislas Wawrinka

As the old head in amongst the young stars, Stan Wawrinka continues to overachieve year after year. Whilst spending his whole career as the Swiss number two behind Roger Federer could have been an annoyance for many, Wawrinka has kept his head down and let his results speak for themselves. A three-time Grand Slam champion in his own right he finished 2016 in wonderful form, defeating Djokovic in the US Open final, and 2017 offers him the opportunity to push for the one major accolade that would seal a wonderful career; the coveted world number 1 spot. A fantastic chance to step out of Roger Federer's shadow and into the limelight for himself.

Alexander Zverev

As the youngest player currently plying his trade in the ATP World Top 50, the 19-year-old Zverev is the wild card superstar and 2017 could be his breakthrough year.

The 6ft 6in German and Junior Australian Open winner Zverev has fantastic potential to be the next generation's leading superstar. With many ex-pros voicing their praise at the young player's abilities, combined with winning his first tour title in St. Petersburg in September 2017 may be the year that men's tennis is refreshed with a new superstar.

Plenty to look forward too!