Nico Rosberg: No Mercedes replacement for retired world champion until new year

Rosberg has said that he is now able to laugh with former team-mate Lewis Hamilton after an intense rivalry on the track

Mercedes will not reveal the identity of world champion Nico Rosberg's replacement until the new year.

The German announced his retirement last month - five days after winning his first world title and despite signing a new two-year deal in July.

Mercedes have the problem of finding a team-mate for Lewis Hamilton when all leading drivers are signed elsewhere.

They want to sign Williams' Valtteri Bottas but have so far not been able to negotiate a deal for the Finn.

A Mercedes spokesman said the team would not reveal any decision before 3 January - and added that did not mean there would be an announcement on that date.

Will Williams let Bottas go?

BBC Sport revealed on Sunday that Mercedes F1 boss Toto Wolff had offered Williams a 10m euro (£8.4m) reduction in their engine bill in return for releasing Bottas from his 2017 contract with Williams.

The team were also given the option of running Mercedes reserve driver Pascal Wehrlein, although this was not a requirement of the deal.

Williams have rejected that first offer but negotiations are continuing and Wolff is expected to make an improved offer.

Williams are aware that Mercedes have money available because they no longer have to spend Rosberg's $22m (£17.6m) salary over the next two years.

The team did admit on Thursday that they would consider letting Bottas leave "if an experienced, credible alternative was available".

One difficulty for Williams is that their contract with sponsor Martini, the drinks giant, requires at least one driver over 25 for promotional reasons.

Their other driver, the Canadian rookie Lance Stroll, is only 18, while Wehrlein is 22.

In a separate development, Mercedes are expected to lose their technical boss Paddy Lowe, who earned about £3m in 2015 and 2016, to Williams. He is set to be replaced by former Ferrari technical director James Allison, but for a lower amount of money.

Who could replace Bottas if he moves?

One option for Williams is to negotiate much bigger financial recompense from Mercedes - perhaps their entire 17m euro (£14.2m) engine fee - and then promote reserve driver Paul di Resta.

The 30-year-old Scot has three seasons of F1 experience with the Force India team.

Di Resta last raced in F1 in 2013, when he beat team-mate Adrian Sutil. In 2012, he scored 46 points to the 63 of team-mate Nico Hulkenberg, who is starting in 2017 a new deal with the factory Renault team.

However, the team do not consider this an option.

The French newspaper L'Equipe reported on Thursday that Williams were in talks about a return for Brazilian Felipe Massa, who retired at the end of the 2016 season after three years with the team.

A senior source says that option was briefly discussed but has been dismissed. However, BBC Sport understands talks are ongoing and it remains a possibility should Bottas leave.

Mercedes are reluctant to promote Wehrlein because they feel he lacks the experience to guarantee scoring the regular big points they will need to defend their constructors' title.

There are also questions over whether the German, who has one season's experience in F1 with Manor in 2016, has shown he has the ability to deserve a race-winning seat.

Their other young driver, Frenchman Esteban Ocon, is committed to Force India in 2017 and with only nine races under his belt has even less experience than Wehrlein.

What about Sainz and Mercedes?

Wolff is also said to have made tentative approaches to Red Bull concerning the availability of Spaniard Carlos Sainz, who is contracted to race for the drinks company's junior team Toro Rosso for a third year in 2017.

Sources say Red Bull are entertaining these conversations, but it is considered unlikely that owner Dietrich Mateschitz would release the 22-year-old.

Insiders say the Austrian billionaire has a long-standing personal enmity towards Mercedes, and it is only just over a year since he believed he had agreed a deal to secure Mercedes engines for Red Bull, only for Wolff and Mercedes to refuse to supply them.

And Red Bull team boss Christian Horner has ruled out selling Sainz to Mercedes.

"Why would we do that?" Horner told BBC Sport. "Carlos has done a great job. He is a Red Bull driver. We have invested in him to get him into F1 and they are all on long-term contracts so it wouldn't make any sense to feed one of your main opponents with one of your assets."