All week long, save for a couple of hours of exertion on a tennis court and shedding more than a few tears when put in her place by her big sister, Serena Williams has been extolling the political virtues of Barack Obama and insisting how the President Elect will make the United States a wonderful place to live.

There are, however, distinct differences between Obama and Serena. He will hopefully stick to both his manifesto and principles and get the job done no matter what personal sacrifice that will take. She once again offered lamely backed away from the challenge, offered her excuses and took her leave with a nice big cheque nestling in her handbag.

Sporting superstars have many obligations to their sport and its extremely generous sponsors, particularly in these worrying times of economic stress. One of those duties is to occasionally refuse to bow to physical pain, guts things out and ensure that everyone gets their money’s worth. Sadly that message has never quite got through to Serena.

In an illustrious if distinctly inconsistent career, she has qualified for the year-ending Sony Ericsson WTA Tour Championships in its present or previous guises on now fewer than eight occasions. Three times she has not even bothered to show up, maintaining injuries: in 1999 the problem was her back, in 2002 her left foot and 2004 her left knee.

Last year in Madrid, she managed to make it through one match (or a set to be more precise) before retiring against Anna Chakvetdaze and pulling out of the event. On that occasion she again cited a pain in her left knee but any agony she may have felt did not stop her staying in the Spanish capital for a week or so sampling everything the shopping and party scene had to offer.

So it is a sad fact of life that nobody was too surprised when Serena announced her inaugural visit to Doha was also going to be cut short to just two matches; a win against Dinara Safina and the emotional drubbing from Venus. This time the ailment is a pulled stomach muscle but it will not prevent her from heading off to South Africa and Kenya on a charitable mission to give out computers to underprivileged school children.

Although Serena insisted she did not feel a twinge of pain during her 5-7, 6-1, 6-0 defeat by Venus less than 24 hours previously, a lunchtime practice session convinced her it was best to submit to the injury. She consulted the tournament doctor and reported: “He definitely, vehemently agreed that it would be in my best interest not to play. So, that helped make my decision a lot easier.”

Serena did not appear to be in any discomfort as she swapped ground strokes with her hitting partner but she maintained serving was an agonising process. And she railed at the suggestion that, given this is the last tournament of the year, perhaps it might have been a professional attitude to play. “Right now I'm really fit,” she stressed. “I just might have tweaked a muscle, which happens. As an athlete, you have to expect that kind of thing. I’ve had this kind of things before. Actually it was in this tournament in 2004 in L.A. And I played through it, and I was out for six to eight weeks and it was awful.”

As is often the case, Serena’s memory plays tricks with her. In fact the quickest glance at the history books will show that within two months of losing that final at the Staples Centre to Maria Sharapova she was en route to winning the Australian Open title, beating a quartet of players ranked 11th, second, fourth and first in the world.

Serena was not alone in throwing in the towel. Ana Ivanovic had been struggling all week with a stomach and throat virus and after losing her initial two matches, it would have been difficult for her to qualify so stepping aside to let first alternate Agnieszka Radwanska face Svetlana Kuznetsova. But Williams still had every chance of joining her sister in the semi-finals and only had to beat Elena Dementieva whose record in this event is hardly exemplary – her win over fellow Muscovite Dinara Safina ending a ten match losing streak.

Jelena Jankovic, confirmed world No 1 for the end of the year come what may this week and another of female tennis’s chronic hypochondriacs, insisted it was not her job to make any comment on whether other players should compete or withdraw. After constantly flexing an aching back and repeatedly blowing her nose in her concluding round robin match against Vera Zvonerva she rightly claimed: “This is the last one of the year. It's the Championships. It's a very big tournament.

"All I can say is that I'm ready to play. No matter what I have, I will try my best to get the little energy I have left in my body, I'm going to give it all and finish the year in the best possible way.”

Apart from celebrating Barack Obama’s electoral victory this week, Serena has again been declaring her love for books. One of the finest and most entertaining sporting works of literature is by the revered American writer Dan Jenkins and called You Gotta Play Hurt. She could do a lot worse than read it on her flight to Africa.