Van der Westhuizen enjoyed an outstanding career
Former South Africa captain Joost van der Westhuizen has been diagnosed with a form of motor neurone disease.
The 40-year-old made his name as one of the world's best scrum-halves during an 89-Test career which saw him secure a World Cup winner's medal in 1995.
He is also his country's joint-record try scorer - with 38 - alongside current Springboks wing Bryan Habana.
His publicist Bridget van Oerle said Van der Westhuizen has a "serious muscle-related neural disease".
She added: "Joost's doctor, who is also a close family friend, noticed that he was having problems with his right arm and ran a series of tests.
"He has also consulted two neurologists and has begun immediate treatment.
"The symptoms are serious and vary from person to person. The media is requested to respect his privacy at this time."
Van der Westhuizen also captained his country at the 1999 World Cup, where they reached the semi-finals, and played his final Test in the quarter-final loss to New Zealand at the 2003 tournament.
He has endured some difficult times during the last few years.
In 2009 he was admitted to hospital after suffering a suspected heart attack after watching a Test between South Africa and the British and Irish Lions, while his marriage came to an end in 2010.
His former South Africa team-mate Andre Venter has also suffered with a form of motor neurone disease and now uses a wheelchair.