Former Springbok rugby player Joost van der Westhuizen has failed to respond to four weeks of treatment according to a statement released by his doctor Jody Pearl.
"Joost (van der Westhuizen) has failed to respond favourably and his neurological symptoms persist but he remains stable. Consequently, the diagnosis of Motor Neuron Disease remains a probability," said Pearl.
It was revealed earlier last month that Van der Westhuizen, 40, was suffering from a life threatening neural disease, but Pearl said it had not yet been fully diagnosed.
"Joost (van der Westhuizen) and I will be travelling to the leading international centre of Neurology at Cleveland Medical Centre in Cleveland, Ohio, USA towards the end of July 2011."
"There we will consult world-leading experts and researchers to assist in finalising Joost's diagnosis and to guide further management," added Pearl.
Van der Westhuizen, a former scrum-half for the Bulls, at one stage held the record for the most Springbok Test appearances. He retired from international rugby in 2003.
(Sapa, June 2011)