Top-ranked Novak Djokovic says winning the US Open to finish a calendar-year Grand Slam would be the greatest feat of his career.

The 34-year-old Serbian has won 20 Grand Slam singles titles, matching Rafael Nadal and Roger Federer for the men's all-time record entering the New York hardcourt fortnight that begins Monday.

Not since Rod Laver in 1969 has any man swept the four major singles titles in one year.

"It's an easy question. Yes, it would be," Djokovic said when asked if the calendar Slam would be his greatest achievement.

"I know how big of an opportunity is in front of me here in New York, where historically I've played really well over the years. It's probably the most entertaining tennis court that we have. Crowd will be back on stadium.

"I can't wait. Honestly I'm very motivated to play my best tennis."

Djokovic called the 2021 Slam sweep possibility a "guiding star" as he chases a fourth US Open crown after 2011, 2015 and 2018.

"I'm hugely inspired and motivated by that, no doubt," Djokovic said. "But at the same time I know how to balance things out mentally, with lots of expectations obviously around."

Nadal and Federer will not play in New York due to injuries, leaving Djokovic to feel the spotlight without his "Big Three" rivals but with three young rising star rivals in Daniil Medvedev, Stefanos Tsitsipas and Olympic champion Alexander Zverev.

"I feel it. I know there's a lot of people who are going to be watching my matches and expecting me to do well and fight for a Slam," Djokovic said.

"At the same time, regardless of Roger's and Rafa's absence, you still have tremendous quality tennis players that are probably right now on hot streak, like Zverev, Medvedev, Tsitsipas, those are the three top contenders I see for the title.

"I've been in this situation numerous times in my life. There's a slight difference in terms of what's at stake and the feeling towards that, but I don't give it too big a significance on a daily basis because I'm trying to be in the present moment."

Djokovic has avoided injury, although he skipped a planned tune-up start at Cincinnati for extra rest after a fourth-place showing in the Tokyo Olympics.

"My preparations for US Open have gone well. I feel good on the court," said Djokovic. "Took little bit of an additional time off after Olympics because I just felt exhausted in every sense after that long summer, which was very successful. Brought a lot of success to me, a lot of confidence."

The pressure of a unique opportunity has proven an inspiration that Djokovic hopes will help him thrive as he has in the past tense situations.

"I'm very inspired to play my best tennis here," Djokovic said. "I don't want to say it's now or never for me because I think I'm going to have more opportunities in my life to win Slams. I don't know if I'm going to be having more opportunities to win calendar slams. That's why it's a very unique opportunity.

"At the same time, I don't need to put any additional pressure to what I already have, which is pretty big from my own self and from people around me.

"But I thrive under pressure, as well. I've done that many times in my career. Pressure is a privilege, it truly is. This is what you work for day in, day out, all your life, to put yourself in a unique position to win Grand Slams and to make history.

"I'm a big tennis fan, fan of history. I admire this sport. I love it. I have this chance and I'm going to try to use it."