An ominous warning has been delivered by French veteran Gael Monfils to the rising stars hoping to dethrone tennis' big three in 2020 – the gap is not closing.

However, it has not stopped 33-year-old Monfils from personally trying to reel in greats Rafael Nadal, Novak Djovokic and Roger Federer this year.

The stage appeared to be set for tennis' new guard to emerge in 2020 after Greece's Stefanos Tsitsipas, 21, became the youngest winner in 18 years of the year-ending ATP Finals back in November.

It came after young guns Austria's Dominic Thiem and Russian Daniil Medvedev threatened in grand slam finals last year.

However, world No.10 Monfils didn't expect the world order to change any time soon.

"I don't know if the gap is closing," he said. "I feel that those top three guys they're still winning quite a lot.

We have a few others winning as well. But with the gap (between the top three and the rest of the field) it's still the same I guess."

It's hard to argue with Monfils after Nadal, Djokovic and Federer combined to win the last 12 grand slams.

Yet Monfils is not discouraged despite his grim prediction, even backing himself to threaten after a landmark 2019.

The former US and French Open semi-finalist enjoyed a renaissance last year, cracking the top 10 for the first time since 2016.

Now he hopes to keep tennis' biggest names honest starting at France's ATP Cup campaign. Monfils was playing Chile on Saturday, but already has one eye on Monday's tie in Brisbane against a Serbian outfit led by Djokovic.

"I had a great year in 2019 and I tried to set my goals a bit higher than it was for last year," the former world No.6 said.

"I really want to be in the top five. I will do anything that's possible…to find the keys to try to get there.

"But it will be hard with the guys that are coming up and also with the older players (top three).

"But I think the top 50 is very strong. So I don't put any pressure on myself – I try to do my best."

Meanwhile, world No.1 Rafael Nadal will be aiming to get his Australian summer off to a hot start when Spain's ATP Cup campaign begins on Saturday night.

Tennis: French star says it's still hard to catch the top three_1
Inset: Rafael Nadal at a practice session for the 2020 ATP Cup in Perth. Photo: AAP

Spain enter the inaugural 24-nation tournament as clear favourites given they will boast Nadal and world No.9 Roberto Bautista Agut in their team.

The defending Davis Cup champions are expected to romp to victory against minnows Georgia in Perth on Saturday night.

Although world No.26 Nikoloz Basilashvili is capable of causing upsets, Georgia's next highest-ranked player is world No. 679 Aleksandre Metreveli.

Bautista Agut will face off against Metreveli, while Nadal is set to take on Basilashvili.

Basilashvili has lost all three of his previous encounters against Nadal, the most recent a 6-1 6-0 drubbing at the 2019 ATP Masters in Rome.

Nadal has the chance to equal Roger Federer's record of 20 grand slam singles titles at the Australian Open later this month.

But the 33-year-old insists the ATP Cup is his priority for now, saying the $22 million event isn't merely a warm-up for the first major of the year.

-with AAP