• Novak Djokovic and Roger Federer

Novak Djokovic and Roger Federer (Photo : Getty Images)

Andy Roddick believes Roger Federer is in the greatest of all time, but the American also admitted Novak Djokovic is gradually joining the "GOAT" conversation.

Roddick, a former professional tennis player and the last American to win a Grand Slam singles title back in 2003 at the US Open, is just one of the many who sees Federer as one of the best tennis players in the sport, having won an all-time record of 17 majors. But the 33-year-old American also thinks Djokovic is in the picture to join Federer in the list of all-time greats.  

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"Right now if you just look at numbers, Roger is obviously there. I think five Slams clear [ahead of Djokovic] is significant. But Novak's obviously trending. He's the greatest right now," Roddick said, reports Tennis Now.

"It's a realistic question to ask: Where do you think he'll fall in the line-up? It's a testament to [Djokovic] that he's kind of forced his way into the conversation."

Federer has already established himself as one of the best tennis players to surface the earth and appears not ready to call it quits yet as he continues his pursuit of an 18th Grand Slam title. However, the last three years have been tough for Federer, who last won a Grand Slam title at Wimbledon in 2012.

This season, Federer was not able to get any traction of winning tournaments, mostly because of injuries and setbacks that prevented him to compete in full health. The Basel native showed signs of post-injury career revival in Church Road, but still fell short of winning the tournament after getting defeated by Canada's Milos Raonic.

On the other hand, Djokovic has had quite the opposite of Federer's campaign in the past few seasons.

The Serb has become a dominant force in the men's tennis scene, winning four of the last five majors, completing his first career Grand Slam. With 12 major titles, Djokovic, who has been at the top of the ATP world rankings for more than 200 weeks, is only a handful of Grand Slams away from surpassing Rafael Nadal and levelling with Federer's record.

Djokovic's chances of a calendar sweep has completely vanished after a disappointing loss at Wimbledon, where the Belgrade native failed to play in full health. But despite a dip in form, the Serb is still primed to win the next Grand Slam event in New York.

Federer and Djokovic could relive their rivalry when both players compete at the the Rogers Cup in Toronto on July 25. A win would put Federer and Djokovic of the two back on the winning track, but more importantly, a victory would give either of the two a chance to reinstate their dominance in the sport.