Yesterday, world No. 1 tennis player Justine Henin did something nobody else had ever done in the history of the Women’s Tennis Association: retire from the game as the No. 1 player.

Henin, who won seven Grand Slam titles amongst her 41 tour victories, was one of the smaller players on tour, barely 5-foot-5. But her fitness and mental toughness allowed her to compete with the new generation of taller, big serving players such as Maria Sharapova and the Williams sisters.

It was, however, expected that her career might be heading downward in late 2006. Her loss to Svetlana Kuznetsova in the U.S. Open came amongst rumors that her marriage to Pierre-Yves Hardenne was unraveling. By the next major, it had.

But the separation seemed to free Henin mentally. She won 10 times in 2007 and reached the final of all four Grand Slam events. She became the first female tennis player to win $5 million in a season.

The end, however, came suddenly for the 25-year-old Henin. Illness, injuries, and reported burnout had Henin in a news conference with a very tearful coach to announce her retirement from the game yesterday.

It is very difficult to see what the landscape of women’s tennis will be like after both U.S. Open finalists from 2003 — Henin and countrywoman Kim Clijsters — retired.

Yes, a flood of players from the former Eastern Bloc are likely to remake the game for some time, led by Maria Sharapova. But you get the feeling you haven’t heard the last of Venus and Serena Williams.

For the last four or five years, their bright lights have been kept under a bowl, as they have used their celebrity to create reality shows, build tennis academies, and have, to their credit, become invaluable ambassadors for the game.

But there’s a big vacuum now in the WTA Tour; who better to fill it?