As the new tennis season is poised to get underway, it would be difficult to mount a convincing argument that 2016 will not go the way of 2015 on the men’s tour, and be dominated by Novak Djokovic. The Serbian superstar is coming off one of the most impressive years in tennis history, winning 11 titles, including three of the four Grand Slams, six of the nine ATP Masters 1000 events and the season-ending ATP World Tour finals.

Still in his prime and with a huge lead at the top of the rankings, it is hard to imagine his place at the summit of men’s tennis slipping. And, now on 10 Grand Slam titles and closing in on the marks of the sport’s all-time greats, he should still have ample motivation.

Instead the bigger question is who Djokovic’s prime challenger will be in 2016. There the picture is not nearly so clear. Andy Murray finished the year ranked second in the world, yet he was well over 7,000 ranking points behind. The Scot has also lost 10 of his last 11 meetings with Djokovic. The two men were born exactly a week apart and their rivalry dates back to their junior days. But of late Djokovic has had the clear upper hand, with his unwavering consistency too much for Murray’s more temperamental mindset.

And what of the only man to beat Djokovic in a Grand Slam in 2015? Stan Wawrinka produced a stunning performance to deny Djokovic the one Major title he has yet to win, when triumphing at the French Open. And the Swiss can never be counted out from producing the sort of power tennis that can break down even the most resilient of opponents. But it is more difficult to envisage the 30-year-old being a consistent threat.

Most doubt surrounds Rafael Nadal. The Spaniard has been Djokovic’s most frequent opponent in his career and given him his most grueling matches. However, Nadal had a hugely disappointing 2015, and he will have to build strongly on the improved form he showed toward the end of the year, as well as maintaining his fitness, to truly challenge Djokovic once again.

Instead, Djokovic’s main competition in 2016 could come from a man who will celebrate his 35th birthday over the next 12 months. Roger Federer may have finished the year at No. 3, but he was the only player to beat Djokovic more than once in the past 12 months. Indeed, Federer beat Djokovic three times in total, including in the final of the Cincinnati Masters 1000 event.

The Swiss also gave him a real challenge in the final of the year’s last two Grand Slams. At both Wimbledon and the U.S. Open, Federer had Djokovic all square after surging back to take the second set. A long-awaited 18th Grand Slam title looked a real possibility. Yet on both occasions, Djokovic proved just too strong down the stretch.

Still, it has to be hugely encouraging for Federer that he is still competing at the very top, against the very best at an age when most players have long since hung up their racket. And in the second half of 2015 he produced some of his best tennis in years. Adopting a more aggressive approach, shrewdly shortening the points against the sport’s dominating baseliners, Federer was rejuvenated. Serving as well as at any point in his career and even adopting a move -- the SABR (Sneak Attack By Roger) -- that became a sensation, he showed he has plenty of life left in him. And, while he has lost the services of his idol Stefan Edberg as a coach, he could be given yet more fresh impetus by Ivan Ljubicic’s arrival to his camp.

The big question for Federer is whether he can get the better of Djokovic over five sets. It is no coincidence that Federer’s three victories all came in matches decided over the best of three sets. If he is to triumph on the stages that matter most then winning the opening set and avoiding getting into a grueling battle is surely essential. Whether Federer can actually dethrone Djokovic and prevent the 28-year-old from further closing in on his record haul of Grand Slam titles, there is reason to believe he has the best shot of anyone out there.