Bottas not guaranteed 2018 Mercedes seat

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Mercedes could dispense with the services of Valtteri Bottas in 2018 given the "dynamic" driver market in Formula One, says Toto Wolff.

The Finn was named as Nico Rosberg's replacement at the Silver Arrows on Monday after Felipe Massa's return to Williams was confirmed.

Bottas has never won a race in F1 but does have nine podium finishes to his name and has already spoken of his confidence of standing on the top step this season.

Wolff has warned that, despite remaining confident in Bottas, Mercedes could change their driver line-up again in 2018 given the options that could become available.

"We wouldn't have chosen Valtteri if we thought that he was not good enough to continue with the team," Wolff told the Formulacast podcast.

"But as a matter of fact, the market is very dynamic at the moment.

"Next year options [are] open - young drivers, Sebastian [Vettel], Fernando [Alonso], Valtteri, many of them. So it is about understanding that, and Valtteri does.

"Equally we have great faith and confidence in him that he can stay with us for a long time but now we need to see how the season goes."

Wolff also revealed on Wednesday that Mercedes had provided financial assistance to enable Massa's return to Williams to go ahead.

"Obviously we couldn't make requests without giving anything in return," he told Gazzetta dello Sport.

"Claire Williams is a really capable businesswoman - like her father Frank. But we didn't only speak about business.

"For example, Williams needed a driver with experience, and it was necessary to get Massa to return.

"So now we are all satisfied - and obviously we have financially contributed to the return of Felipe."