Mercedes boss Toto Wolff has admitted his team were caught out by Nico Rosberg's decision to quit last year and will try to ensure it has a contingency plan in place should a similar situation arise in the future.

Rosberg unexpectedly walked out of Formula 1 after securing a maiden world championship in November last year. The decision wrong footed Mercedes and while the German team quickly secured Valtteri Bottas from Williams, the Finnish driver is only under contract until 2018.

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"It's easier to solve problems that you saw coming, but the Nico thing came out of nowhere, at a time when most of the drivers already had contracts for the following year," Wolff said in an interview with Autosport.

"It was not easy. We knew that we had [test driver] Pascal [Wehrein] as a possibility, but he's probably too young to burn him in a car that is capable of winning races against the best driver on the grid."

Lewis Hamilton's deal will also expire next year and, given nothing has yet been formally agreed with either driver, Wolff said Mercedes would not be taking anything for granted following last year's experience.

"There is certainly a component that in F1 you need to have a fall back solution, a plan B," he added. Even having a contract doesn't necessarily mean that everything is going to be like it is. There could be a change of circumstances. What we have now is a plan A, and then there is obviously various possible plays afterwards, because the driver market changes a lot in 2018 and 2019. It is important to consider plan B and C."

Nico Rosberg and Lewis Hamilton
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Aside for Hamilton and Bottas, a number of other drivers will be out of contract either this season or the next, which could further complicate the circumstance for teams to looking to retain their drivers.

While admitting the situation was "very complex", Wolff added having a number of drivers available to change team could also work in Mercedes' favour.

"There are many possibilities where a driver could end up," he explained. "There are certainly at least a handful of capable drivers who would perform in a Mercedes. So you have to consider all scenarios."

Should any of the Mercedes drivers decide to walk away from the team, Wolff hopes having a plan B will minimise the disruption and make it easier to replace one of them than it was to sign Bottas.

"Valtteri was our primary candidate, but obviously Williams was keen to keep him," he added. "And it wasn't the only factor. It was multi-faceted - there was also if we could agree on a financial compensation with Williams.

"Who would they take? What would happen to Pascal? At the same time undoing the Nico contract. Finally to have achieved the outcome that was our most preferred option was good."