The Italian, who had both his legs amputated after a motor racing accident almost 20 years ago, had been recovering in hospital after suffering a horrific cycling crash in June.
He initially underwent three hours of emergency neurological surgery and was placed in an artificial coma.
On Tuesday, a month following the accident, Zanardi was moved to a rehabilitation center after his sedation was ended but, on Friday, it was confirmed he had been transferred to the intensive care unit of the Milan San Raffaele hospital due to his “unstable clinical conditions.”
Claudio Zanon, health director of the Valduce Hospital, said in a statement that “no further information on the case will be released.”
The Italian is an incredibly popular figure. He had been in training for this year’s Tokyo Paralympics before it was postponed, hoping to add to his impressive tally of gold medals.
Among the many messages of support, Pope Francis wrote him a letter whilst he continued his recovery in hospital. He praised Zanardi for living life to the fullest and for providing a “lesson in humanity.”