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The winner of 18 Grand Slam singles titles said the Williams sisters were the star attraction for the women's circuit, but they needed to provide support to tournaments outside the four majors.
"We have two superstars who do not play as much as they should or could... Imagine if (Roger) Federer and (Rafael) Nadal only played 12 tournaments a year, it would be 'Where are they?'," she told AFP.
"Serena does not play enough and Venus plays, but still not as much as she should," she added.
Serena Williams pulled out of the Madrid Masters on Monday during her first round match after criticising new WTA rules that specify you have to play a certain number of tournaments a year.
"You have to support the tour, for years the Grand Slams have been getting too much attention," Navratilova added.
She insisted that the women's game was in good health and said the fact a large number of players were capable of winning big tournaments was a good sign.
"People are more ready to criticise (the women's game). For example when Chris (Evert) and I were dominating, people said there was not enough competition," she said.
"Now you have so many different Grand Slam winners, people are saying the sport does not have any superstars - what do you want?"
Navratilova was in Hong Kong to sell some of her artworks - created by bouncing tennis balls dipped in paint on canvasses with Slovakian artist Juro Kralik - with the proceeds going to the Sovereign Art Foundation, which raises money for disadvantaged children.
