Claire Williams has revealed that Valtteri Bottas is close to joining Mercedes as a replacement for retired world champion Nico Rosberg.

The German shocked the sport by calling time on his career less than a week after edging out teammate Lewis Hamilton to win the title last year.

Mercedes have been on the lookout for a replacement since, with their original plan to have a new driver in place by Christmas delayed, but Bottas is now expected to depart Williams and join the Silver Arrows by the end of next week.

"It has been dragging on and I think everyone wants to know, probably more who is going to be Lewis's teammate next year, and of course whenever Nico made his announcement we knew the call was probably going to come from Toto [Wolff]," chief executive Williams told Sky Sports News. "It is a great opportunity for Valtteri and he has given a lot to Williams.

"We've always said if we can make this happen on terms that are positive for Williams then it is probably the right thing to do. Nobody needs or wants a driver in your team that really wants to be somewhere else. It is not nice either to stop a driver who has such a great opportunity, particularly at this point of Valtteri's career, but it has to work for Williams and that is what we've been working hard on over the past six weeks.

"We are nearly there, we are at the tail end of it and hopefully we'll be able to make an announcement this coming week. But it has to be right for Williams, whatever we do will always be the right decision for Williams no matter what other people's opinions might be."

Williams are reportedly looking to bring Felipe Massa out of retirement to replace the outgoing Bottas, with some experience required alongside rookie Lance Stroll for the season ahead.