Formula One must slash costs by 2010 or face serious problems, FIA president Max Mosley warned yesterday.

The Briton told the BBC that the global credit crunch had only made matters worse for the big-spending sport and there was a serious risk of some teams walking away if matters were not taken in hand.

"It has become apparent, long before the current difficulties, that F1 was unsustainable," he said.

"It really is a very serious situation. If we can't get this (the cost cutting measures) done for 2010, we will be in serious difficulty."

One team, Honda-backed Super Aguri, has already folded this year while others are either bankrolled by billionaires or owned by car manufacturers against a backdrop of reduced sales and falling share prices.

"At the moment we've got 20 cars," said Mosley. "If we lost two teams, we'd have 16. (If we lost) three teams (we'd have) 14. It then would cease to be a credible grid."

Williams chief executive Adam Parr told Reuters last week that some of the teams could save around $200 million a year if they reduced their spending to the same level as the former champions.

Toyota are widely estimated to spend more than $400 million a year on a team that has yet to win a race.