Roger Federer is the king of tennis, don't know why Novak Djokovic's father comments on him: Stefan Koubek

Novak Djokovic has come under fire for many different reasons over the last few weeks, even as professional tennis looks set to return amid the COVID-19 pandemic.

The Adria Tour, hosted and funded by the Serb and members of his family came to a halt after four players, including Djokovic himself, tested positive for COVID-19. To add fuel to the fire, Djokovic's father Srdjan has been in the news for his his comments about his son's achievements and rivalry with Roger Federer.

Srdjan Djokovic claimed that the World No. 4 was jealous of his son and couldn't cope with the fact that he has been surpassed by the Serb.

Novak Djokovic's father, who is known to have made outrageous statements in the past as well, added that Roger Federer "cannot accept that Rafael Nadal and Novak will overtake him." The elder Djokovic also advised the 20-time Grand Slam champion to spend more time with his family and 'go skiing' instead of playing tennis.

Suffice to say these comments did not go down well with the tennis world. And Stefan Koubek, Austria's Davis Cup captain, has ripped into Srdjan and claimed that he does his son no favors.

Don't know what Novak Djokovic's father wanted to do with his comments on Roger Federer: Koubek

Roger Federer (L) and Novak Djokovic at Wimbledon 2019

As reported by Swiss new outlet Blick, Koubek laid into Novak Djokovic's father and claimed that his comments on Roger Federer were totally out of order.

"There are things that can be saved," the Austrian said. "I don't know what Papa Djokovic wanted to do with it (his comments on Federer). Novak himself can say that. I don't know why the environment always gives out such things."

The rivalry between Novak Djokovic and Roger Federer reached its peak during last year's epic Wimbledon final which Djokovic edged in five memorable sets and the first ever deciding set tiebreak on the grass at SW19. With Roger Federer's recent injury, and the form of Rafael Nadal and Novak Djokovic, the Greatest of All Time (GOAT) debate has been reignited by many fans.

There are plenty of doubts about whether the Swiss legend will be able to replicate his form after injury. For Koubek, however, there is only one out-and-out GOAT, and he did not mince his words about it.

"Roger Federer is the king of tennis, the (best) player of all time," asserted Koubek, before requesting the World No. 4 to play longer. "If he's still playing, that's good for everyone. Please play for another five years."