CNN  — 

Kim Clijsters will have to wait a little longer to make her high-profile return to tennis.

Clijsters sustained a knee injury and said she won’t be able to compete at the Australian Open in two months.

“I’ve had to make the decision that I will not be able to compete in January,” the four-time major champion and former world No. 1 wrote in a tweet Monday.

“I am undergoing rehab and treatment for a knee injury. It’s a setback but I’m determined as ever to get back to the game I love. I really appreciate all your support and encouragement.”

In September, Clijsters announced she was ending her retirement and coming back to tennis at age 36.

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She last played competitive matches when she was 29 at the 2012 US Open. Following her retirement then, the Belgian was inducted into the International Tennis Hall of Fame as a member of the class of 2017.

This will be Clijsters’ second comeback to the sport. She first made a successful return to the WTA in 2009, winning three of her four major titles – the US Open in 2009 and 2010 and the Australian Open in 2011 – after losing her first four grand slam finals.

With her US Open win in 2009, Clijsters became the third WTA player to win a major after giving birth, following Margaret Court and Evonne Goolagong. She returned to the No. 1 spot in the world on February 14, 2011.

“While there is a lot of work ahead of me in the next four months, my biggest motivation is the personal challenge involved – both physically and mentally, I want to test myself again,” Clijsters said in a press release when she revealed her comeback plans.

“At 36 years old I feel like I’m too young to be retired and, with so many inspirational athletes and moms competing, I can’t wait to get back on the match court and see what’s possible after having three children.”

Clijsters made her WTA debut age 15 at Antwerp in 1999. She won her first major in 2005 at the US Open. In May 2007, she stepped away from the sport, marrying US basketball player Brian Lynch and giving birth to her daughter Jada in 2008. She also has two sons, Jack (born in 2013) and Blake (born in 2016).

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Clijsters owns 41 career singles titles and 11 career doubles titles. As a former world No. 1 and grand slam champion, Clijsters will have access to unlimited wild cards.