Former world No. 1 Caroline Wozniacki will return to the Singapore Indoor Stadium to defend her singles title at the Oct 21-28 BNP Paribas WTA Finals Singapore presented by SC Global.

The Dane and Petra Kvitova of the Czech Republic qualified for the season-ending event yesterday, joining world No. 1 Simona Halep, Wimbledon champion Angelique Kerber and US Open winner Naomi Osaka.

However, it is unknown if Halep will make the trip, after she said earlier this week that she has a herniated disc after a scan on her back.

Three more spots are up for grabs for the last edition of the tournament in Singapore, before it moves to Shenzhen, China next year.

Wozniacki, who won her maiden Grand Slam title in January's Australian Open, beat Venus Williams to win the WTA Finals last year.

Said the 28-year-old: "I'm very happy to qualify for the WTA Finals. Winning the WTA Finals last year was a huge accomplishment for me, and helped my confidence leading into this season. I look forward to coming back to Singapore to try and (retain) my title."

Kvitova, also 28, is making her sixth appearance at the WTA Finals after a Tour-leading five titles this season. The 2011 champion is making her return after she was attacked in her home by a knife-wielding intruder in 2016.

"It's a huge honour to qualify for the WTA Finals again," she said.

"It will be my first time back there since I came back to tennis so it means a lot to me and has always been one of my big goals for the season."

The WTA Finals Singapore is a 10-day tennis festival featuring the world's best players vying for US$7 million (S$9.6 million) in prize money.

The top eight singles players will compete in a round-robin format with the winner taking home the Billie Jean King Trophy.

The top eight doubles teams will compete in a knock-out format for the WTA Finals Martina Navratilova Trophy.

• Tickets are available at wtafinals.com