Webber: Rosberg Frontrunner for Williams

"I think he is, but that's just my opinion," the Australian said at the Brazilian Grand Prix on Thursday. "Frank (Williams) is talking about other people but I would think he would be frontrunner."

Williams have a vacancy after Briton Jenson Button bought his way out of the contract he signed last year and signed a long-term deal to remain at BAR.

Germany's Nick Heidfeld, who has been Webber's teammate for most of the season, is moving to BMW. The German carmaker has bought the Sauber team and is ending the partnership with Williams.

Brazilian Antonio Pizzonia will race in Brazil after standing in for Heidfeld at the last two races but there has been talk in the paddock of 20-year-old Rosberg being drafted in for the final races in Japan and China.

The Germany-born son of Finland's 1982 World Champion, who won the title with Williams, is a test driver already and has impressed in the junior GP2 series which acts as a feeder for Formula One.

Webber, who has yet to have a teammate partner him for more than one season since his debut with Minardi in 2002, said that he was "losing zero sleep" over who the team would sign.

"Obviously there is a spare seat there next year and Nico's done a good job in testing...clearly he's on the list, no question about it," said Webber.

"I think Antonio is very well known, they know what he can do. He's been here for four years. Nico's been here for four months. Nico's young, but beyond his years really."

Were Williams to put their faith in Rosberg, it would be a situation similar to that in 2000 when they gave Button his debut as a 20-year-old.

However, whereas Button came in from British Formula Three, Rosberg knows the European circuits already after doing a season as part of the Grand Prix circus with the GP2 cars.

"With Jenson, it would have been good for him to be here for so many reasons. He's not, so we have to get the next long-term charger in and if it's Nico that's great," said Webber.

The Australian said Button's determination to remain at BAR was another blow for Williams, who have also lost principal sponsor HP while also changing tyre provider from Michelin to Bridgestone.

"It's a real shame he's not coming," he said of Button. "This time last year I was very excited at the idea of Jenson coming here.

"There's been many knocks and that's just another one. But we'll roll up at Bahrain next year and it will be all forgotten. It's very quickly water under the bridge."