Button has had a superb season

The BAR driver is in third place, 10 points adrift of the Ferrari driver, prior to Sunday's US Grand Prix.

He said: "Second is a target and to beat a Ferrari would be a very big achievement but it's going to be tough.

"It would be nice to catch up with Rubens but he is driving the best car on the grid, so it's a bit difficult."

Despite a series of podium finishes this season, Button has yet to claim his maiden F1 victory.

We know how to improve the car but it can't happen overnight Jenson Button

But he insists he is unconcerned about a lack of a win to date.

"Before this year I hadn't got a podium, so there's no frustration there at all at the moment that I've not won a race," he added.

"But if I pick up seconds and thirds for the rest of the season then I will be second in the championship, so that's not a bad position to be in.

"It would certainly be nice to get a bit closer to the Ferraris, and I'm sure we will, but we can't just make that leap, it does take a lot of time and effort.

"We know where we want to be and we know how to improve the car, but it can't happen overnight. It takes time and hopefully we will be there in a few races."