Williams, who bid an emotional goodbye to tennis at the US Open last month, and seven-times Olympic gold medalist Felix both had businesses up and running before calling time on their careers.

Other elite female athletes, such as four-time WNBA champion Sue Bird and three-times Olympic ice hockey medalist Kendall Coyne Schofield, have leveraged their experience in front offices of professional sport.

King, who battled for gender equality in tennis and celebrated her Women's Sports Foundation's annual gala this week, told Reuters the next stage of their careers would be just as rewarding.

"Money gives you opportunity, flexibility, mobility and also helps things grow," she said. "And that's why men have always done so well ... like the old boys network.

"Well, we're starting to get an old girls network and that's really important."

Felix built her own shoe brand 'Saysh' during the COVID-19 pandemic and Gap Inc took an equity stake in June, while 23 times Grand Slam champion Williams' venture fund announced in March that it had raised $111 million.

"I think (Williams') second half of her life will be much more exciting in some ways, not as far as performance, but investment," said King.

King and wife Ilana Kloss have a stake in National Women's Soccer League team Angel City FC, along with Williams and husband Alexis Ohanian, as well as Major League Baseball's Los Angeles Dodgers.

Five-times Olympic gold medalist Bird, who retired this year from the WNBA and co-founded the digital media company Together last year, worked in the front office of the National Basketball Association's Denver Nuggets.

Coyne Schofield, whose playing career is still going strong, became the first female player development coach for the National Hockey League's Chicago Blackhawks in 2020.

"You really don't know who's going to take over but what's starting to happen, which is fantastic, is these athletes are going to work for professional sports organizations after their career or even during their careers," said King.