Niki Lauda says that "practically half" of the F1 grid has been in touch with Mercedes to offer themselves as a replacement for retiring world champion Nico Rosberg.

After winning his maiden F1 title in Abu Dhabi last weekend, Rosberg shocked the F1 world when he announced his retirement from the sport during the FIA Gala Awards in Vienna on Friday.

This left Mercedes with a vacancy to fill alongside Lewis Hamilton for next season, albeit at a time when only Sauber and Manor have not announced their driver line-ups for 2017.

Speaking to Gazzetta dello Sport, Mercedes non-executive chairman Lauda admitted that Rosberg's sudden exit had left the Brackley-based squad "disorientated".

Asked when he knew about the news, Lauda said: “A few hours before the public announcement. He told us by phone. I took it badly, I didn’t expect it, nobody in Mercedes imagined that he had had enough.

“At first I didn’t believe it. ‘Nico, what you told us, are you kidding by any chance? It’s a joke?’ But he said it was all true. Quite incredible.

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"When I won the first title I immediately thought about how I would win a second. Not the case with Nico.

“Rosberg’s decision has left us disorientated and unprepared, and all those who contributed to Nico winning the world title took it very badly."

Lauda says the fact most top drivers are under contract elsewhere makes the task of replacing Rosberg especially difficult, and that taking a young driver - such as Pascal Wehrlein - would be a "risk".

"We have lost a champion, the best driver of 2016," added Lauda. "It won’t be easy to replace him because all the drivers of a certain standard have contracts with other teams.

“Taking a young driver is a risk, we don’t know if he will be strong. Practically half of the grid have offered themselves.”

Gallery: Lauda: "Half of the grid" has offered to replace Rosberg

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