Germany's seven-time Formula One champion Michael Schumacher admitted on Wednesday he had doubts ahead of his historic comeback but also that uncertainty was a secret to his success.

"I always had doubts in myself before, even in the good years," 41-year-old Schumacher, who returns after a three year hiatus at the season-opening Bahrain Grand Prix with Mercedes GP on Sunday, told Germany's Stern magazine.

"I think that this is part of the reason for my success - constantly looking for new areas where I can improve."

Following his break, "Schumi" also said he has "found out how to have fun again, something which I had lost".

And in case anyone wondered, the German, winner of 91 Grand Prix in 250 starts, was crystal clear what his goal was this season: an eighth drivers' title.

"Of course. It goes without saying," he said.

"That's why I signed a three-year contract."

Dieter Zetsche, the chairman of the Daimler group and the head of Mercedes-Benz, was also bullish, saying his team had "probably" the best management, the best drivers and the best engines.

"We've got all the ingredients for a superb recipe. Now all we have to do is cook it right," Zetsche said.

Observers do not necessarily share his confidence, with Schumacher having to contend with a new crop of drivers keen to teach the German a lesson and send him back into retirement.