American world number one Williams has bagged 19 singles slams, the most recent coming at this year's Australian Open.
Logic suggests that, at 33, time is running out but Navratilova, who won 18 singles majors, believes the way Williams plays is key to her chances of reaching the milestone.
"It's possible, given the way she plays," Navratilova said in an interview in The Independent on Tuesday.
"It's fast tennis. She doesn't have to grind it out: big serves, big returns. The trick for players (playing against her) is to get into the point with her.
"But if anyone can do it, it will be her, with her technique and her physique and her mental ability and drive."
Navratilova, who recently ended her coaching role with Poland's Agnieszka Radwanska, said Williams had flourished since joining up with Frenchman Patrick Mouratoglou three years ago, winning six of the last 11 grand slams since.
"She seems to believe in herself more," Navratilova said. "The biggest difference I see from the outside is her steadiness
"She allowed herself to evolve with his help. She's really trusted him to make the changes or adjustments."
(Reporting by Martyn Herman, editing by Ed Osmond)
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