Nico Rosberg says he wants to win a world championship with Williams, but also does not rule out switching to another team to achieve his ultimate F1 goal.

The German driver, who turned 23 recently, is set to remain at the British team in 2009, but interestingly points out that contracts are no guarantee about the future.

Asked by Germany's Sport Bild is he is 100 per cent sure he will be driving the FW31 next year, Rosberg replied: "I have a contract."

Pressed further, he explained: "It's like in football; take (German player Lukas) Podolski.

"He signed a contract for next season at FC Bayern -- but will he be there?"

Rosberg was strongly linked with Fernando Alonso's vacated McLaren Seat for 2008, but ultimately signed a lucrative extension to remain at Williams through to the end of 2009.

Sport Bild asked the driver about the possibility that other teams will again enquire about buying out his contract.

"The first thing would be Frank Williams," Rosberg explained. "I would only begin to think about it if Frank agreed to release me."

He said his "100 per cent" objective is to become world champion.

"If I can't do it with Williams, I just have to go to a team where it is possible."

Rosberg admits he has been disappointed by Grove based Williams' trajectory in the opening half of this season.

"At the start we were looking really good, but we were not able to have the development progress of the top teams," he said.

"I know that next year I will not win the title with Williams, but I do hope for a big step forward.

"With the new regulations, particularly the cutting back of the aerodynamics, it means everyone starts from scratch basically. Without that, I would have my doubts," he said.

Sport Bild said it sounded as if Rosberg sees 2009 as a final chance for Williams to turn around its form.

"You could say that," the German admitted.

Source: GMM