Tennis fans in Doha, Qatar, are used to seeing Serena and Venus Williams at the WTA Championships. Each sister has won the season-ending title, and coming into this year's event, their images were everywhere around the city.

Both were no-shows last week, though, because of injuries. And both will also miss this weekend's Fed Cup final in San Diego between the United States and Italy.

Sidelined by two operations on her right foot after getting cut by glass at a restaurant, Serena Williams hasn't played a competitive match anywhere since winning Wimbledon on July 3. Hobbled by a bad left knee, Venus Williams has only played in one tournament, the US Open, since losing at Wimbledon.

Serena turned 29 this year, Venus turned 30, and while neither has given any public indication she is contemplating retirement anytime soon, their extended absences have given other players, fans, WTA officials and TV networks a chance to see what it is like to have a women's tennis tour without the famous siblings.

WTA chief executive officer Stacey Allaster described the Williams sisters as "two of the most exciting and finest players we have had in our history," but insisted the tour can remain strong without them.

"Every time there is changing of a generation of stars... it's very natural for all of us to say 'Who is next?' Allaster said.