It is understood doctors are taking every precaution given the serious nature of Lauda's surgery.

Austrian Lauda, 69, was given his transplant in August after doctors found he had "severe lung disease".

Doctors said after the transplant that he would have had between three and seven days to live without the surgery.

Lauda, a Mercedes F1 non-executive chairman, has legendary status in F1 not just for his 25 race wins and three championships - two with Ferrari and one for McLaren - but his recovery from a fiery accident at the 1976 German Grand Prix.

Lauda was given the last rites after he was trapped inside his burning Ferrari at the Nurburgring, suffering severe burns to his face, hands and lungs. He raced in Italy 40 days later.

Doctors said the illness this year was not a consequence of the accident.