Jackie Stewart insists it is unrealistic to expect the British Racing Drivers' Club (BRDC) to foot all the bill for the improvements needed at Silverstone.
The Northamptonshire track's future as host of the British Grand Prix is under threat after Formula One chief Bernie Ecclestone's repeated criticism of Silverstone's facilities.
Ecclestone was also unimpressed by the incident in Sunday's race that saw a man run up the Hangar Straight.
Ecclestone has given the BRDC, owners of Silverstone, a month to commit themselves to a £40 million sterling upgrade of the circuit or risk losing their place on the Formula One calendar.
BRDC president Stewart believes that deadline is "unrealistic" as it does not allow adequate time to find partners to help with finance, which could include the Government.
Stewart told BBC Radio 5 Live: "The BRDC, a private club, are being asked to raise this money. It is not possible to occur, but we don't mind being among the players. Those players could include the British Government.
"It has to be proportional. I do not think four weeks is realistic but the BRDC is keen to play a proportional part".