Ashleigh Barty has not played since her third-round defeat to Shelby Rogers at the US Open in September ©Getty Images

World number one Ashleigh Barty of Australia has opted not to defend her Women’s Tennis Association (WTA) Finals title after bringing her season to a premature end.

Barty cited the COVID-19 travel and quarantine restrictions in her home country as one of the reasons for her decision.

The 25-year-old said she also wanted to focus on preparing for the start of next season as she bids to win the Australian Open for the first time in January.

Barty calls time on a season that saw her win five titles including a second Grand Slam crown at Wimbledon in July.

Despite not playing since September’s US Open, where she lost in the third round, Barty is guaranteed to finish the year as world number one.

The Australian captured the WTA Finals crown in 2019 and remains the reigning champion after last year’s edition of the season-ending event was cancelled because of the COVID-19 pandemic.

This year’s WTA Finals are due to be staged in Mexican city Guadalajara from November 10 to 17 after being moved from Shenzhen in China because of coronavirus restrictions.

"I wanted to let everyone know that I won't be competing in any further tournaments in 2021, including the WTA Finals in Mexico," Barty said in a statement.

"It was a difficult decision but I need to prioritize my body and my recovery from our 2021 season.

"With ongoing challenges of traveling back to Queensland and quarantine requirements, I am not willing to compromise my preparation for January.

"I wish the WTA team and the players all the best for a successful WTA Finals and the rest of the year."

Ashleigh Barty will finish the year as world number one after winning five titles this season including her first women's singles Wimbledon crown ©Getty Images
Ashleigh Barty will finish the year as world number one after winning five titles this season including her first women's singles Wimbledon crown ©Getty Images

Barty missed both the US Open and French Open last year due to fears over the risk of contracting COVID-19 and did not play in a tournament outside of Australia for more than a year until April’s Miami Open.

It was confirmed earlier this week that players who are not fully vaccinated against coronavirus in time for the Australian Open will be denied entry into the country.

The move casts further doubt over the participation of men's world number one Novak Djokovic.

The 34-year-old Serbian, who is seeking a record 21st Grand Slam title and 10th Australian Open crown, is opposed to mandatory COVID-19 vaccines and refuses to reveal whether or not he has been innoculated.

Barty believes Djokovic is entitled to keep his vaccination status secret.

"I didn’t feel there was a need for me to tell everyone whether I was vaccinated or not," Barty told the Courier-Mail.

"I have been vaccinated my whole life.

"I think players are entitled to... at the end of the day it's part of your medical history. 

"You understand people make decisions for different reasons and you have to respect that.

"From my point of view it’s personal to me.

"I had my vaccine in April.

"I was fit and healthy and I was doing it for the people around me to make sure we were safe.

"There is no judgement for me or necessity for me to see what others have done."