Serena Williams heads for 2010 as world number one, WTA Championships, Australian Open and Wimbledon champion, but there's a worrying storm gathering over women's tennis.

The new year should spark a celebration of marquee match-ups where the Williams sisters renew their epic rivalry with the returning Kim Clijsters and Justine Henin.

Hopes are also high for a fully-fit Maria Sharapova to grace more tennis courts than red carpets, while Caroline Wozniacki and Victoria Azarenka lead the new generation.

Williams pocketed 1.55 million dollars for relieving sister Venus of her WTA Championships title here on Sunday, but it wasn't the only mind-boggling sum giving the WTA headaches.

The deadline for a renewal of the tour's 88-million-dollar, six-year agreement with title sponsor Sony Ericsson is the end of the year, but the global financial crisis is never far from sports' front doors.

"We are looking at our sponsorship seriously. We haven't made any decision yet, and all options are open," said Aldo Ligouri, vice-president and head of global communications at Sony Ericsson.

When the deal was signed in 2005, it represented a much-needed boost for the WTA, which had been without a title sponsor in 2003 and 2004.

However, Ericsson recently reported a 74-percent fall in net profit blamed on falling sales and problems at its Sony Ericsson venture.

If that wasn't enough, there are signs that the WTA Roadmap, designed to protect the long-term health of its top stars, may not be having the desired effect.

The 4.55 million dollar WTA Championships featured the world's top eight players.

By the end of the week, however, 10 had taken part with one alternate even being replaced by another.

Tearful Dinara Safina lasted just two games and 12 minutes, losing her world number one spot while Wozniacki and Azarenka quit before the end of their involvement.

Serena played the final with her left thigh bandaged; Venus needed protection for her left knee.

"We definitely weren't physically a 100-percent today. But it just shows you how much we try," said Serena, who blamed physical exhaustion on her decision to withdraw from the US team to face Italy in the Fed Cup final.

In 2009, players saw their WTA tournament commitment cut from 13 to 10.

Both Williams sisters have played 16 events, including the four Grand Slams; Wozniacki played 90 matches in a year which saw her reach the US Open final and reach four in the world.

"We were asking the athletes to play 13 commitments, and they're down to 10," said Stacey Allaster, the WTA chief executive.

"If we don't have healthy athletes, you know, we can't have a level of product that we want."

While Serena flies into 2010 as world number one, 29-year-old Venus knows time is ticking.

The holder of 41 titles, it's been eight months since she last held up a trophy and she looked sluggish in Doha, squeezing into the semi-finals despite losing two of three round-robin encounters.

However, she will enter her 14th year on the tour determined to prove that she still has a role to play.

"I hope I will be completely healthy. Hopefully, some luck will be with me and bad luck with someone else," said the American.