Sebastian Vettel admits Mercedes just too strong

Four-time world champion Sebastian Vettel admitted Thursday that Ferrari are a "big gap" behind Mercedes and need the champions to struggle if they are to beat them.

The German driver is 43 points behind defending champion and series leader Lewis Hamilton of Mercedes in the drivers` title race.

"We have to be realistic," he told a news conference on the eve of opening practice for this weekend`s Austrian Grand Prix.

"Challenging Mercedes, we know we need to have a flawless weekend, a perfect weekend and maybe them to have a bit of a struggle.

"But with normal circumstances they are still favourites and there is quite a big gap."