McLaren has to shoulder blame, says Dennis

Speaking in Autosport magazine, Dennis said: "The drops of rain that fell just as he made his second (Suzuka) pit stop lost us the race, but championships aren't won or lost in one race."

Hakkinen's McLaren-Mercedes suffered engine failures in the season-opening Australian and Brazilian Grands Prix, with a third engine failure at the United States GP effectively ending his realistic title chances prior to the title-deciding race at Suzuka. But Dennis believes that metal and physical fatigue also played a significant part.

"I think we sideswiped him to have had the failures after leading both of the first races," he said. "That blunted the edge, although I don't think either he or we knew at the time.

"We really intensified the testing. As a result of that I think both drivers were drained, both physically and mentally and a little more so with Mika than David. The consequences were that he lost a bit of motivation through mental fatigue.

"As I said at the time, I was disappointed in my own performance for not having been able to to recognise the problem sooner," he added. "I think Mika also struggled with mid-season car characteristics. But I don't think that was a significant factor: the main problem was a bit of mental fatigue, which we induced. It wasn't a shortcoming on Mika's side."

Mercedes sports boss Norbert Haug said after the Japanese GP that the Stuttgart marque and its engine builder Ilmor would need to raise its game next season.

McLaren can still win the constructors' championship at this weekend's season-closing Malaysian race. But with Ferrari needing just three points to guarantee it a drivers' and constructors' title double, the Woking-based squad looks likely to end its season without a title for the first time since 1997.