Eight of the 13 year-end world number ones invited did show up at the STAPLES Center for an on-court ceremony to honour tour founder Billie Jean King and the other founding members.

But the Williams sisters -- plus Steffi Graf, Arantxa Sanchez-Vicario and Monica Seles -- were conspicuous by their absence.

"You're part of the history and the present and future. It's too bad they (the Williams sisters) didn't make it. I know Serena is in town... I don't know where Venus is," Navratilova said. "They should have been here."

The sisters had attended a Los Angeles Lakers game and a fashion show in the city earlier in the week.

WTA officials weren't sure why the five absentees, who earned a combined $78 million prize money, didn't come.

"I don't know what everyone's situations were, but I would be disappointed if there were some that could have made it here and didn't," added Chris Evert who enjoyed a hypnotic rivalry with Navratilova spanning three decades. "That would be too bad.

GOOD EXCUSE

"But if you can't, you can't. Steffi could have jumped on her or (husband Andre) Agassi's private plane. I would hope you have a really good excuse if you didn't come."

Graf recently gave birth to their second child, a daughter, Jaz. Even though the German travels with Agassi on tour, she almost never makes public appearances to promote tennis.

"Steffi doesn't talk much," Navratilova. "She keeps to herself. I never really had a conversation with her. I think she's asked me about four questions in my life, so how can you have a conversation?

"She never really gave much of herself to anyone on the tour. She's not going to start now. She supports Andre, but even there she is in the background, in the corner and not on camera. That's how she is and that's okay."

Those in attendance included Evert, Billie Jean King, Navratilova, Tracy Austin, Martina Hingis, Jennifer Capriati, Kim Clijsters and this year's year-end world number one Justine Henin-Hardenne.