Paris - Former world number one Kim Clijsters has been forced to delay her planned return to competitive tennis in January following a seven-year hiatus because of a knee injury.
The 36-year-old four-time singles Grand Slam champion in September announced plans of a surprise comeback ahead of the Australian Open in 2020.
"I've had to make the decision that I will not be able to compete in January," Clijsters tweeted.
"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."
Clijsters' manager Bob Laes, cited by Belgian daily Het Nieuwsblad, said she "made a wrong move during a workout and felt pain" from an injury he described as a medial ligament tear.
She faces "six to eight weeks of rehabilitation" before she can resume intensive training, Laes added.
Clijsters won the US Open in 2005, 2009 and 2010, and the Australian Open in 2011.
She initially retired in 2007 aged 23, making a return two years later after having her first child to win her second US Open, then hanging up her racquet again after the 2012 US Open.
Clijsters made her WTA debut aged 15 at Antwerp in 1999. She has 41 singles titles, and is the only mother to top the WTA charts since computer rankings began in 1975.
Despite her lengthy time out she still ranks third among active players in terms of tournament success behind the Williams sisters -- Serena with 72 titles and Venus with 49.