A statement on the J9 Foundation's website confirmed he was in hospital.
"The family and friends of Joost ask that you all pray for Joost. He was taken to hospital earlier today and is in a critical condition."
Van der Westhuizen‚ who has been fighting motor neuron disease since 2011‚ played 89 Tests for the Springboks between 1993 and 2003.
The former Springbok was diagnosed with a form of Motor Neuron Disease in 2011 and recent pictures shared by his estranged wife‚ Amor Vittone‚ showed he has been deteriorating.
Two weeks ago it was revealed that Joost was now on an oxygen machine. At the time it was reported he was on the machine to survive‚ but Joost downplayed these reports‚ saying he was "doing well under the circumstances."
Since being diagnosed‚ the 45-year-old former rugby star has spoken publicly about his illness‚ insisting that he will fight until the end.
Family members have told TshisaLIVE that Joost's manager and friend are in the ICU ward with him at a Johannesburg hospital.
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