Nico Rosberg is the son of former world champion Keke

Webber said Finn youngster Rosberg - the son of former world champion Keke - had shown promise during testing.

"It's a shame Button is not joining - it would have been great to have him here," said the Australian.

"Nico has done a good job in testing. He's on the list, no question about it. He's young but he is beyond his years."

Button made it clear he no longer wanted to drive for Williams and eventually escaped his deal after protracted negotiations.

Webber added: "Jenson's heart was not going to be here.

I think they are very similar, Jenson and Nico Mark Webber

"I can understand the situation he is in, in that he has got everything he wants down there.

"He is in a situation when he's got the speed, the results and the whole team working for him, he doesn't want to leave."

Rosberg has been racing in the GP2 series that supports Formula One and is on the verge of beating Renault-backed Finn Heikki Kovalainen to the title.

"I think they are very similar, Jenson and Nico," said Webber.

"Jenson was a bit more fast-tracked than Nico because he came straight from Formula Three whereas Nico has had a season of GP2 at all the circuits."