Ferrari president Luca di Montezemolo admitted the reigning Formula One champions face a mighty battle to retain their title.

The Italian team, who have won the last four constructors' titles, dominated the season last year with 15 wins in 17 races, but the present campaign has been anything but a cakewalk.

Williams secured a one-two finish at the European Grand Prix on Sunday to move into second place in the championship race and keep the heat on Ferrari.

McLaren, whose Finnish driver Kimi Raikkonen may well have won the race had his car not suffered engine failure, are still in the hunt, trailing Williams by just six points.

"I said at the start that it would be a difficult year," Montezemolo said.

"After the Canadian Grand Prix some people wrote off the McLaren team, but instead they had a brilliant race last Sunday.

"Williams have made enormous progress and so have their tyre suppliers. How could anyone think that this would not be the case with some of the greatest companies in the world working for some of the biggest names in motor racing.

"And above all there is a great hunger for victory as they have haven't tasted it for four years."