Mercedes steered away from signing Pascal Wehrlein for 2017 because it would have been "too early" for the young German, according to Toto Wolff.

Wolff, who went on to sign Williams's Valtteri Bottas instead, told Italy's La Gazzetta dello Sport that he was not already thinking of Bottas's name when Nico Rosberg announced his shock retirement.

"No. First of all, it was necessary to evaluate all the options on the driver market. We needed an experienced and fast driver," he said.

Asked why that was not Wehrlein, the 22-year-old cream of Mercedes's development programme, Wolff said: "We decided that it was too early for him to become Lewis [Hamilton]'s teammate.

"For Pascal and Esteban Ocon we have our own programme, designed for two or three years."

For 2017, Wehrlein is instead heading to Sauber, a Ferrari-powered team.

Asked if this means that Sauber could switch to Mercedes power for 2018, Wolff answered: "No, the contracts with the drivers are in no way connected with the engines.

"We respect the partnership between Sauber and Ferrari."

What Wolff would admit is that getting Bottas out of his Williams contract, involving pulling Felipe Massa out of retirement to replace the Finn, cost Mercedes money.

"We could not make them an offer without offering anything in return," he said.

"Claire Williams is a smart businesswoman. But we talked not only about financial matters. Williams also needed an experienced driver and Felipe had to be persuaded to return. But in the end everyone is happy."

Asked if Mercedes is paying for Massa's return, he confirmed: "Yes, obviously."

However, Wolff said his focus is now on getting Bottas up to speed, as after that process they "expect that he will be able to drive at the level of Nico Rosberg".

"We need him and Lewis to motivate each other and get the atmosphere that provoked the performances of Nico and Lewis," said Wolff.

Asked if Hamilton-Bottas could be as good as Hamilton-Rosberg but without the conflict, Wolff answered: "I hope so."

As for the controversy about Bottas's mere one-year contract at Mercedes, Wolff played that down.

"If Valtteri fights for the world championship in 2017, or if he becomes world champion, then he will stay with Mercedes," he is quoted as saying by Bild newspaper.

The 2017 championship begins with the Australian Grand Prix in March.