Former No. 1 Kim Clijsters, now 36 years old, planning return to tennis

Seven years after retiring from tennis a second time, Kim Clijsters is attempting another comeback at age 36.

The former No. 1 and four-time major champion, who already is a member of the International Tennis Hall of Fame, announced Thursday she is planning to return to the pro tour in 2020, although she's not yet ready to say exactly when or where or how often she will compete.

"My goal right now ... is to be able to get fit enough, and ready tennis-wise, to compete at the highest level. That to me would be my challenge, as of right now. And if you get to that stage, then you push yourself, and then it might be like, 'Hmm, let's see if I can get, I don't know, to the second week of a Grand Slam.' I'll constantly push myself, I think, if I feel that I'm getting better and improving," Clijsters said.

"But it's very hard for me to think about right now, and very unrealistic at this stage, to think, 'I want to try and get to a quarter-final of a Grand Slam,"' she said. "I don't think like that, because I'm in the moment, and I know how much work I still have ahead."

Clijsters turned pro in 1997, won the U.S. Open for the first time in 2005 and walked away from tennis in 2007 at just 23, shortly before getting married to an American basketball player, Brian Lynch.

After about two years away while having a daughter, Clijsters returned and soon won the 2009 U.S. Open, making her the first mother to collect a Grand Slam singles title since Evonne Goolagong at Wimbledon in 1980.

With a baseline game built on terrific court coverage, the Belgian won another championship at Flushing Meadows in 2010, then added an Australian Open title the following season and moved back atop the rankings.

Clijsters, who now has three children, left the tour again in 2012 and has been working as a television broadcaster.

"I do think the level and the power that a lot of the women bring is higher than maybe in the past, and it's higher at a consistent level," she said. "If I want to be able to compete with these girls, I'm going to have to be the fittest that I ever have been and to be able to move like I did in the past."

Documentary in the works

She said the earliest stages of her comeback bid have been filmed by a documentary crew for the past six months, although she decided for sure to give this a real try only in recent weeks.

WTA rules allow her, as a past Grand Slam champion, to receive unlimited wild-card invitations to tournaments and, as someone who is older than 30, to opt out of mandatory appearances at certain events.

"I know that I'm not going to play — not even close to — a full season," Clijsters said, adding that her intention is to be ready for January.

Clijsters said having her kids in school allowed her to get back on a practice court during the day.

"I have girlfriends now who, at times, struggle to find 'me' time and find their passion and find the time to live for their passion and still balance being a mom. And I do feel like ... 'Me, too.' I'm 36 years old. I know in four years, I'm not going to be able to do this," she said. "I've always followed my instincts. I was very young when I retired to have my first daughter, and came back. To do it now, I think, to me, is a challenge. And I love the challenge. I'm not afraid of it."