Serena Williams has vowed to come back fit and healthy in 2016, after opting out of the final two tournaments of the year.

The world number one, who has won three Grand Slam titles this year, says she is taking time away from the game to recover fully from elbow and knee problems, while also admitting that missing out in the semi-finals of the US Open had been a major blow to her morale.

She told the official China Open website: “I’m a fierce competitor and I want to compete as well as I can, for as long as I can.

“So I am taking a proactive step and withdrawing from tournaments in Beijing and Singapore to properly address my health and take the time to heal.”

Williams was on course for a calendar grand slam before being ousted in the last four at Flushing Meadows by Roberta Vinci, while her decision means that she will miss the chance to top the season off with victory at the WTA Tour Championships in Singapore.

She is the three-time defending champion and has won the season finale on no fewer than five occasions, triumphing for the first time way back in 2001, while she has also lost in the final twice.

Maria Sharapova is also a doubt for the Singapore tournament, having already withdrawn from the China Open due to an injury to her left arm.

Sharapova was forced to withdraw during her clash with Barbora Strycova at the Wuhan Open, having only just returned to the court after being sidelined since Wimbledon due to a leg problem.

Meanwhile, Great Britain are 1.37 to win the upcoming Davis Cup final, with hosts Belgium 3.00.