World No 1 Novak Djokovic will up the ante in the 2020 Tokyo Olympics as he chases history and bids for an Olympic title in Tokyo. Ahead of the opening ceremony, he said that he never truly believed winning a calendar Golden Grand Slam would one day be possible.

But as days go by, he thinks winning a calendar Golden Grand Slam is "more and more realistic."

He will be seeking to emulate Steffi Graf's unrivalled achievement from 1988 when she won all the four majors and won gold in the women's singles in Seoul. To date, the Serbian has won at the Australian Open, Roland Garros and Wimbledon.

"I have utmost respect and admiration for Steffi and everything she has achieved in her career and the mark that she left in our sport," Djokovic said.

"When I was thinking about the ultimate achievement that she had, which was the four Slams and Olympic gold medal in one year, I did not think that it would be, I don't want to say achievable, but that there's a slim chance that someone could make it again, male or female."

"Right now it seems more and more realistic for me. Of course that's one of the goals and dreams, but it's hard to compare sports and circumstances back in the days that she played and now," said Djokovic.

"But still, the champion's mentality she (Graf) possesses is definitely something that inspires me so hopefully I'll be able to use that in my upcoming tasks."

Tokyo 2020 Olympics will be without Rafael Nadal and Roger Federer, making Djokovic the clear favourite for the Olympic crown.

Djokovic won bronze at the 2008 Olympics in Beijing but missed out on a medal four years later following a defeat by Juan Martin del Potro.

Djokovic joked he was "relieved" not to see Del Potro in this year's tournament, and said it was a "bit strange" to be playing an event without Nadal and Federer, having equalled their record of 20 Grand Slam titles at Wimbledon.

"I have not had too many big tournaments in the past 15 years without Roger and Rafa playing, so it's a little bit strange because I'm used to seeing at least one of them," said Djokovic.

"But still there are some of the best players in the world here.

"(Daniil) Medvedev, (Stefanos) Tsitsipas, (Alexander) Zverev and Andrey (Rublev) -- they're top six, seven in the world and they're the biggest candidates for winning a medal."

Djokovic, who conceded he felt nervous at previous Olympics, will start his campaign against Hugo Dellien, the world number 139 from Bolivia.

"I'm going to approach it like it's a normal tournament," said Djokovic.

"I've already arguably had the best Grand Slam season in my sport so far. I could not have a better lead-up to the Olympic Games than I've had this year.

"It's still a very long way to a potential historic achievement. I've put myself in a very good position.

"I know there is a lot of things on the line, I know there is history on the line, but I'm privileged and motivated to be in this position, I've worked very hard to be there.

"But let's talk abut history if everything goes great here after I finish with the tournament."