Djokovic won his 20th Major at Wimbledon a few weeks ago. He is now level with Roger Federer and Rafael Nadal at the top of the Grand Slam leaderboard. Given Djokovic's form and physical capabilities, many believe the Serb will end up winning a few more Majors by the time he decides to retire.
Navratilova, an 18-time Slam champion in singles, reckons Djokovic is fit enough to continue playing for another three to four years and can thus end up with "somewhere between 23 and 25 Majors".
"Somewhere between 23 and 25. I'm settling on 24," Navratilova told Tennis.com. He's a young 34-year-old and he's still got another three or four years left, and you've got to figure he'll win at least one a year, so yeah, maybe even more. But 24 is a good number I think (for Novak Djokovic to end up with)."
During the conversation, Navratilova also weighed in on Naomi Osaka's prospects at this year's US Open, where the Japanese is the defending champion.
Osaka lost in the third round of the Tokyo Olympics, but Navratilova believes the Japanese can bounce back strongly and win the US Open.
"I think she (Naomi Osaka) has a very good chance of repeating and winning the US Open for the third time," Navratilova said.
Navratilova then shifted her focus to Serena Williams. The American reckons the 23-time Major champion is unlikely to win more than one Grand Slam over the rest of her career.
"24 is very possible," Navratilova said. More probably not. I thought she had a great shot at Wimbledon. Didn't happen. If she's healthy then US Open is her best shot at it other than Wimbledon. It's about a 50-50 proposition at this point."
Stefanos Tsitsipas is most likely to be a future Major champion: Martina Navratilova on Novak Djokovic's biggest challengers
Turning her attention to some of Novak Djokovic's challengers in men's tennis, Martina Navratilova said she considers Stefanos Tsitsipas best-equipped to win a Slam in the future.
According to the American, even though Daniil Medvedev is the higher-ranked player, Tsitsipas is a better bet to win a Major as he has a more complete game.
"The obvious answer to that (most likely future Slam winner) would be Medvedev, since he's ranked No. 2 in the World but I'm going to go out on a limb a little bit, a little bit lower, and go with Tsitsipas," said Navratilova. "I think he's got a more complete game, and I think he's got the tools. We'll see."