Paris - Australian tennis legend Rod Laver, the last man to hold all four Grand Slam titles at the same time twice, backed current world number one Novak Djokovic to repeat the feat at this year's French Open.

The now-80-year-old Laver won calendar Grand Slams in 1962 and 1969, the first year all four majors were professional, to write his name into the history books.

But Serbia's Djokovic, who first held all four when he won his maiden Roland Garros title in 2016, is hunting him down after adding the Australian Open trophy earlier this year to his 2018 Wimbledon and US Open titles.

"I'm probably favouring Novak at the moment and then Rafa (Nadal) and then it goes down the line. Then it's who's going to play who," said Laver on Monday.

"I marvel at someone like Novak with his ability and his consistency."

Laver, an 11-time Grand Slam title winner, also thinks Djokovic is capable of becoming the first man since himself 50 years ago to win a calendar clean-sweep.

"He's won all four at one time or defending champion at all times, so he's already done that portion of it," he said.

"But I think more so when I look at today, he just won the Australian, so, now he's in line to win a Grand Slam.

"It's a long way to go, he's only got one, but this is probably, for him, I would think, it's probably the toughest.

"You just have to be very fortunate and play your best tennis at the right time, no injuries, no sickness, no colds, over a nine-month circuit."

Djokovic, 32, has now won 15 Grand Slam titles in total, two fewer than Nadal, who turned 33 on Monday, and five adrift of record-holder Roger Federer.

The 37-year-old Federer is playing at Roland Garros for the first time since 2015 and will face Stan Wawrinka in the quarter-finals, while Nadal is preparing for a last-eight clash with either Japan's Kei Nishikori or Benoit Paire of France.

Laver says there is nothing to separate the three as they chase the all-time record major tally before retiring.

"You look at their record, which is really how you summarize who the best players are. And I think Novak is certainly equal to - I think you look at three of them, you look at Novak and Rafa and Roger. To me, they are three just huge champions.

"I think all of them are just brilliant on the court."