Novak Djokovic has admitted he is “sad” that most of his long-term rivals have retired from tennis. The 24-time Grand Slam winner namechecked Andy Murray, Roger Federer and Rafael Nadal before appearing in an exhibition match in Buenos Aires to mark Juan Martin del Potro’s retirement.

Djokovic claimed his first Grand Slam title at the Australian Open in 2008 and has won more Major titles than any other man in the history of the sport.

But his powers appear to be on the wane and it is only a matter of time before he too calls time on his illustrious career.

Djokovic was full of melancholy as he prepared to face Del Potro, who was forced to quit the sport two-and-a-half years ago after failing to recover from a serious knee injury.

And after being asked if the encounter marked the end of an era, the Serbian explained: “Yes and no. I am still playing and I believe I am part of a golden era.

“Federer, Nadal, Murray, Delpo, [Stan] Wawrinka, it is a very special era for our sport. Our personal careers have been influenced by all these rivalries of the last 15 years. For me, looking at this year, it is an incredible thing. I am a bit sad because my greatest rivals have left.

“A part of me, in terms of tennis, also leaves with them, but I continue to seek this motivation. Now I work with a new coach, one of my biggest rivals, who inspires me to see if we can achieve great things in our sport.”

Djokovic is still focused on winning more titles before putting his racket down for good and appointed Murray as his coach last weekend.

And discussing the link up with the Briton, Djokovic told Sky Sports on Friday: “I was going through a process of thinking about next season in the past couple of months and figuring out what I needed as I stopped with my coach Goran Ivanisevic, who I was successful with.

“I took about six months to think if I really needed a coach and if yes, who is that going to be and the profile of the coach.

“We were going through different names and I realised at this point the perfect coach would be someone who has been through the experiences I have been through.

“A multiple Grand Slam winner and I was thinking about a few and the Andy Murray discussion appeared on the table with my team. I decided I would give him a call and see how it goes.

“It caught him off guard a little bit as he wasn’t expecting it. We connected really fast and he accepted it after a few days. I can’t be more excited about it.”