After a solid season for Williams, Rosberg sits seventh in the 2009 championship
Nico Rosberg has revealed that he is leaving Williams at the end of the season, with the German driver expected to race for Brawn GP in 2010.
The 24-year-old would not comment when asked to confirm that he had done a deal with Brawn's engine supplier Mercedes, which had secured him a seat.
"It is my last race for Williams so it's a bit strange," he said, ahead of Sunday's final 2009 race in Abu Dhabi.
Rosberg is likely to swap places with Brawn's veteran Rubens Barrichello.
"I've been with the team for five years," added Rosberg.
I'm not sure they [Williams] can win races at the moment, and I would like to win races
"They're the only team, I've worked with. [Team boss] Frank Williams, especially, [chief executive] Adam Parr, [technical director] Sam Michael, [co-owner] Patrick Head have really supported my career over these years and I'd like to say a very big thank you to them.
"There's no reason why they can't be as good as this year (next year). But I'm not sure they can win races at the moment, and I would like to win races.
"It's been a good season because the team gave me a good car it was an opportunity to raise my share value and to find a winning car for next year."
In August, Rosberg put himself forward as a potential team-mate for world champion Lewis Hamilton at McLaren if Heikki Kovalainen left.
But with German car giant Mercedes interested in purchasing a considerable stake in the Brawn team, it is believed they want a native driver to drive for the new world champions.
Mercedes are said to be looking at buying a stake of as much as 75% in Brawn.
If that deal goes through, it is considered likely that Mercedes would sell the 40% stake in McLaren it has owned since 1999.
But in that event, it is understood that Mercedes would continue as McLaren's engine supplier.
A McLaren spokesman denied on Thursday rumours claiming the team might buy BMW's engine project following its decision to quit F1 at the end of the season.
"Stories linking McLaren to any deal concerning BMW's engine operation are complete rubbish," he told BBC Sport.
BMW motorsport boss Mario Theissen echoed McLaren's denial.
Rosberg has landed two podium finishes in his 69-race career, but just missed out on improving that record this season with fourth places in both Germany and Hungary.
Barrichello, who was Jenson Button's main challenger for the 2009 world title before his team-mate clinched the crown at the last race in Brazil, has been in talks with Williams over a one-year deal.