Toto Wolff has admitted that Valtteri Bottas needs to prove he should keep his new seat at Mercedes beyond 2017.

Unusually for a top team, Mercedes have signed only a one-year deal with the Finn.

Wolff admitted to Germany's Auto Motor und Sport that the short deal leaves Mercedes's options open in the event that Sebastian Vettel, Fernando Alonso, Sergio Perez and Carlos Sainz might be available for 2018.

"Of course," said the Mercedes boss.

"Nevertheless, we would like the Bottas solution to work and the question of a new driver will no longer be posed.

"But as you can see from Nico [Rosberg], tomorrow's situation can be different from today's. We'll see how Bottas compares with Lewis [Hamilton] and how the other drivers are going as well. Also our own boys at Sauber (Pascal Wehrlein) and Force India (Esteban Ocon).

"There are a lot of options for 2018 onwards."

Wolff also played down Mercedes's loss of their technical chief Paddy Lowe, saying that the team is "very strong" in terms of other technical personnel.

Asked if Lowe's successor will be the Ferrari refugee James Allison, he answered: "We will have to wait, but of course, James must be on the radar of every top team."

Finally, Wolff responded to those who say that although the chassis and tyre rules are changing dramatically for 2017, it will be Mercedes's engine that continues to set the pace.

"At the end of last season, the difference between the power units was only one and a half tenths," he said. "So it could be less than a tenth this season. Then it will be again be more about the chassis."

The first grand prix of the season will be in Melbourne on March 26.