BBC Sport
Alex Zanardi has had a second operation as a result of the severe head injuries he suffered in a hand cycle accident.
The 53-year-old Italian, a former Formula 1 driver turned four-time Paralympic gold medallist, collided with a lorry during a race in Pienza, Italy, on 19 June.
A hospital statement said the surgery was "necessary" after "an evolution of the patient's state".
It added that his neurological condition remained "severe".
Roberto Gusino, health director of the hospital in Sienna, said of the two-and-a-half-hour surgery: "The intervention carried out represents a step that had been hypothesised by the team.
"Our professionals will evaluate the evolution of the situation day by day. In agreement with the family, the next bulletin will be released in about 24 hours."
Zanardi remains in intensive care, where he is sedated and intubated. His cardio-respiratory and metabolic condition is "stable" and his prognosis is confidential.
Zanardi has become a global sporting icon for the strength of will and determination he has shown in overcoming adversity in his career, after he lost both his legs in an accident while racing in a Champ Car event in Germany in 2001.
Zanardi drove in F1 from 1991-94 and in 1999, for the Jordan, Minardi, Lotus and Williams teams, scoring a best result of sixth place.
He raced in the US-based Champ Car series from 1996-98, winning the title in 1997 and 1998.
He returned to Champ Cars in 2001, when he lost both his legs in an accident at Germany's Lausitzring.
After extensive rehabilitation, he returned to motorsport in 2005, spending four years racing for BMW in the World Touring Car Championship, and winning four races.
He then turned to hand-cycling, in which he has won 12 world championships in addition to his four Paralympic gold medals, as well as the New York City marathon in 2011.