Dr. Giuseppe Olivieri said former Formula One driver Alex Zanardi is in a "serious but stable" condition following a road accident in Italy, adding the operation went according to plan.
Zanardi was airlifted to the Santa Maria alle Scotte hospital in Siena after a shocking crash with a large vehicle while riding his handbike on Friday.
The 53-year-old suffered a horrifying motorsport accident in 2001 that resulted in both of his legs being amputated above the knee.
Olivieri provided an update on Zanardi after undergoing surgery for severe head injuries amid grave concerns for the 2012 and 2016 Paralympic gold medallist, telling reporters: "The condition of Alex Zanardi is serious but stable.
"He arrived here with major facial cranial trauma, a smashed face, and a deeply fractured frontal bone [forehead]. The numbers are good, although it remains a very serious situation.
"We won't see what his neurological state is until he wakes up — if he wakes up. Serious condition means it's a situation when someone could die. Improvement takes time in these cases.
"Turns for the worse can be sudden. The operation went according to the plan. It's the initial situation that was very serious."
Olivieri added: "The next step is to try and stabilise him over the next week or 10 days. Then if things go well, he could eventually be woken up and re-evaluated.
"As I told his wife, he's a patient who is worth being treated. As far as a prognosis of how he'll be tomorrow, in a week or in 15 days, I don't know. But I'm convinced that he should be treated."