Novak Djokovic believes there is "room for improvement" regarding the prize money available to players at the four Grand Slams.

Tournament prize money has been a contentious issue this year, after the top 20 men's and women's players signed a letter asking for a greater share of revenue from the Australian Open, French Open, Wimbledon and US Open.

Earlier this month, the United States Tennis Association announced a 20% increase in prize money for the US Open - creating what is claims is "the largest purse in tennis history' - with $90m (£67.4m) in total up for grabs.

"Look, it's a step in the right direction," Djokovic, 38, said on Friday when asked if the increase mirrors what players had in mind.

"Obviously, it's always nice and positive to see that Grand Slams are willing to improve the prize money overall across the board for the players.

"Whether it's an ideal situation for us, I think overall, I don't think so. I think there is still a lot more room for improvement in that sense."

Djokovic explained that he doesn't want increases for himself, but for players lower in the rankings who rely on Grand Slams.

"I see that in the past when I talk about this topic, people like to say, 'Well, look at him, wanting more money for himself'. It's not about that," said the 24-time Grand Slam winner.

"I'm just talking about overall. Not many tennis players live out of this sport globally. That's not something that I see has been talked about enough.

"It's also important to understand that we live in a very commercial world. Entertainment and sports business are very big.

"And for Grand Slams, they are doing very well as well. So the US Open increased the prize money. Other slams are doing it too. But they also have a bigger revenue than the previous year.

"Then there is the inflation part, which is a completely different topic, but important to take in consideration when you talk about these things.

"Overall it's definitely a positive step."

Earlier this year, the Professional Tennis Players' Association (PTPA) launched legal action against tennis' governing bodies, citing "anti-competitive practices and a blatant disregard for player welfare".

The lawsuit by the players' group, which was co-founded by Djokovic, sought an end to what it describes as "monopolistic control" of the tennis tour, as well as financial compensation from the ATP, the WTA, the International Tennis Federation (ITF) and the International Tennis Integrity Agency (ITIA).

Djokovic subsequently said that "there are things that I agree with in the lawsuit, and then there are also things that I don't agree with".

Djokovic will begin his US Open campaign on Sunday against American Learner Tien at Arthur Ashe Stadium in Queens, New York City.