The Springbok scrum-half had been battling the disease since 2011 and was admitted to hospital on Saturday 4 February according to his J9 Foundation.
The foundation has been posting updates on his condition on Facebook. He was in a critical condition on Saturday, but was stabilised although being on life support.
President Jacob Zuma released a statement over the weekend urging South Africans to pray for the former Springbok player. The statement read: “Mr Van der Westhuizen is one of the best rugby players that the country has ever produced. We are saddened by his ill health. We urge the nation to keep him and his family in their thoughts and prayers.”
Van der Westhuizen was diagnosed at the age of 40 and was given two years to live. He spent the last few years of his life fighting the disease and creating awareness around it through his J9 Foundation.
He was part of the triumphant South African Rugby team at the 1995 Rugby World Cup and was inducted into the International Rugby Hall of Fame in 2007. He represented South Africa in 89 test matches, scoring 38 tries.
The rugby legend played at three Rugby World Cups (1995, 1999, 2003), the Tri-Nations Cup (1998) and won two domestic Currie Cup trophies (1998 and 2002).
Tweets have begun pouring in remembering the sports legend:
Sad to hear the news on #joostvanderwesthuizen a true inspiration on and off the pitch.
— Jack Llewellyn (@GarethJack) February 6, 2017
RIP #joostvanderwesthuizen , true legend of the game! What a player!
— Tom Davies (@tomdaviesgolf) February 6, 2017
Man, so heartbreaking. Thoughts & Prayers with the family. Joost, you will always be a South African hero. #RIP pic.twitter.com/42KiQF8vFP
— Brent Lindeque (@BrentLindeque) February 6, 2017
SA will forever love and remember you! ???????????? #RIPJoost #joostvanderwesthuizen #sarugby
— Lauren Kate (@itslaurenkayte) February 6, 2017
#RIP Joost at least now you dont have to suffer anymore…… #joostvanderwesthuizen #Rugby #Springboks pic.twitter.com/GOVPsfj3Q2
— Best of the Cape (@needham_brad) February 6, 2017
The Springbok Rugby page posted a moving tribute for van der Westhuizen on Facebook:
Watch this video below made by the J9 Foundation: