Toto Wolff has admitted it is possible Valtteri Bottas could be replaced at Mercedes by a bigger name for 2018.

Some expressed surprise when it emerged that, despite being prised out of his Williams contract, Finn Bottas has signed only a one-year deal for 2017.

Mercedes chief Wolff admits it is to leave the team's options open for 2018.

"It is true that the driver market is more dynamic for 2018," Marca sports newspaper quotes him as saying.

"Then there are a number of options: young drivers, Sebastian (Vettel), Fernando (Alonso), Valtteri, and more.

"Valtteri understands this," Wolff added.

Former Red Bull driver Robert Doornbos is more blunt as he assesses the situation in conversation with Dutch broadcaster Ziggo Sport Totaal.

"Bottas is an interim solution," he said.

"Basically Mercedes is looking at Vettel. Only if Bottas wins the title, or makes it very difficult for Hamilton, will he stay."

Doornbos says Bottas was once "really hot property", but his star faded a little at Williams when "the gap to Felipe Massa was in my view smaller than it should be".

So even Wolff admits that Bottas now needs to prove he belongs at Mercedes this year.

"He must demonstrate that he can fight against Lewis (Hamilton)," he told the French daily L'Equipe.

"For us, his personality is perfect, as it was important not to upset the dynamics of the team," said Wolff.

"Valtteri is not at all political or emotional, but his passion for racing is enormous. It will be interesting to see the dynamics between him and Lewis."

Asked if Bottas can actually beat Hamilton, however, Wolff answered: "It's difficult to say when the new cars haven't turned a wheel.

"Valtteri is an exceptional driver and has the ability to push Lewis as Nico did. We believe in him. But can he beat the best driver currently in F1? I don't know."

(GMM)