Novak Djokovic and Andy Murray's ability to match Roger Federer and Rafael Nadal in 2017 will depend on their fitness, according to Paul Annacone.

The Serb and the Scot are currently recovering from elbow and hip injuries, respectively, and have not played competitively since their loss at Wimbledon in July this year. Djokovic and Murray decided to end their season early and focus on getting back to full fitness similar to what Federer did last season.

The Swiss ace ended his season after Wimbledon in 2016 before making a strong comeback in 2017. Similarly, Nadal also ended his 2016 campaign in October and returned to action in January.

Federer and Nadal won a combined 13 titles this year, including equally sharing all four Grand Slams and there has been much talk if Djokovic and Murray can do the same. Annacone, however, believes that their health will hold the key to them competing with the best in 2018.

The former world number one's will start the New Year as the number 12 and 16 ranked players, respectively, and overall have been backed to return to winning ways. However, it remains to be seen if they can emulate the two greats — Federer and Nadal — of the current era, who turned back the clock in 2017 with some nostalgic performances, especially in their respective victories at Wimbledon and Roland Garros.

"I would think so. I don't know how healthy Novak and Andy is but when you start playing three out of five sets especially with their style of play, where they don't get a lot of free points, they are working hard from day one, we are going to see how healthy they are early on," Annacone said, as quoted by the Express.

"And if they are healthy, they are great players. Great doesn't just stop, especially at their age. They are not all of sudden not great anymore.

"There's no reason why Djokovic and Murray can't be at the top of the game with Federer and Nadal next year," Federer's former coach explained.