New WTA CEO Steve Simon will make "fundamental" changes to the cramped end-of-year tennis calendar to ensure the best players compete at the flagship WTA Finals after world number one Serena Williams withdrew from this year's event.

In this March 22, 2015, photo provided by BNP Paribas Open, Steve Simon gestures before the start of the women's tennis final at the BNP Paribas Open in Indian Wells, Calif.  [Photo/Agencies]

The American's absence because of fatigue is a hammer blow for organizers, who have been welcoming tired players to Singapore this week after frantic efforts to ensure qualification for the lucrative end-of-season event.

Simon, formerly Tournament Director and Chief Operating Officer of the Indian Wells event, said calendar changes were likely to be a hot topic of conversation when he sat down with the players this week.

"We have to make some fundamental changes in the calendar and our approach to it," he told reporters in Singapore on Monday.

"We have to look at our structure and look at what we do to give the athlete the best chance to be as close to 100 percent at the end of the year as they can."

Russia's Maria Sharapova beat Agnieszka Radwanska in her WTA finals opener on Sunday in the first match she had completed since losing to Williams at Wimbledon in July.

Radwanska and fellow Singapore competitors Simona Halep and Petra Kvitova have also had injury issues this year which will go on after Singapore despite the end of season tag.

Zhuhai, China next week will be the 59th event of the calendar before the season closes the following week with the Fed Cup final. A brief off-season then takes place before the players return to tournaments in the first week of January to start another grueling campaign.

Martin Navratilova, winner of 59 grand slam titles, said it was too long.

"I still think overall we see the number of injuries and withdrawals is still too high," she told reporters on Monday.

"Maybe it's great to have all these tournaments, but at the end of the day, if you don't have enough players playing, you got a problem.

"So I still think for me it probably would be the length of the calendar that's a long‑term project. I was talking about that 35, 30 years ago. The season is too long."

In Sunday's WTA Finals opener Romanian Halep thumped US Open champion Flavia Pennetta 6-0 6-3. The Italian was likely to have been fatigued after a hectic recent playing itinerary including China and Moscow in a desperate bid to qualify for Singapore.

Simon said he was unsure how he would change the schedule following the U.S. Open in September but said it was necessary.

"The players are tired coming out of the US Open. It's been a long season and they've played a lot of tennis," he said.

"Then you exacerbate it when you have a compelling race that's forcing them to play even more to try and get here.

"What we do with it is the $99 question that we have to resolve and figure out how to do it. But we do need to address that."