It may have finally broken into the top ten in the F1 constructors' standings, but Marussia's future remains uncertain.

That is the claim of Mercedes' executive director Toto Wolff, who revealed that the Banbury-based backmarker was still pursuing merger talks with mid-grid rivals.

The 2013 pre-season was rife with the suggestion that Marussia might move in with fellow minnow Caterham - a proposal apparently favoured by F1 ringmaster Bernie Ecclestone as he looked to trim the field to just ten teams - but talks broke down amid shareholder fears.

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"I can confirm that discussions took place, [but] I wasn't involved in them and, as I understand it, the conclusion was unacceptable to our shareholders, so nothing happened," Marussia's Graeme Lowdon told Sky Sports Online in March.

Now, however, Wolff has claimed that Marussia continues to investigate merger options and has spoken to both Williams and Sauber about the possibility of joining forces. The Austrian has an interest in talks between Marussia and Williams as he remains a stakeholder in the Grove team, despite moving to Mercedes last winter. Following Williams' stock market flotation, his 12.2 per cent stake is reckoned to be worth around EUR22m, but Wolff insists that a merger is unlikely to happen.

"It would close Marussia, it would close Caterham or whatever," he was quoted by ESPN, "That's why those discussions are getting nowhere."

Wolff, who took a 30 per cent interest in Mercedes along with his executive director role, insists that he is still looking to off-load some or all of his shares in Williams. The stake had been linked to former Mercedes team principal Ross Brawn, but Wolff admits that he has not yet found a buyer.

"I do not have a deadline," he confirmed, "It is absolutely flexible. The intention is to sell them over a reasonable period of time."

"I would never do anything against the interests of Frank [Williams]. I need to find the right partner. I need to have somebody who is not only buying those shares, but who is buying for the family and who is potentially a sponsor or brings some added value to Williams.

"The difficulty is that you don't want to find somebody who is just pouring money into it. It's a catch because you need to find somebody who feels that it is an investment but, at the same time, hopefully has a brand which he wants to promote. If you find that kind of person, then it makes sense."

Wolff said that he could understand why the owners of Marussia might want to find another team to merge with, despite the team achieving its best-ever finish in four years of F1. Last year, the sport's smallest team reported a ?59m net loss, while changes to the regulations for 2014 are set to increase costs massively ahead of its next financial report.

"You have a high profile, wealthy individual who funds a team with 50, 60 or 70 million a year but, performance-wise, is not getting anywhere," Wolff explained, "Then you have a team which is self-funded where you could buy a substantial minority stake, five per cent or maybe more, and you could go on to the board. At the same time, instead of paying 50, 60, 70 million a year, you pay 20 or 30 and you promote your own brand. "

In January he jumped ship to Mercedes and took a 30% stake in that too. Soon afterwards he announced that he would dispose of his Williams shares to avoid any conflicts of interest.

Despite suffering its own reversal of fortune on track in 2013, and seeing major sponsor PSVSA follow Pastor Maldonado to Lotus for 2014, Wolff insists that Williams remains financially sound.

"Williams was always healthy and even though, let's say, profits have somehow flat-lined, it is still a company that has generated positive cashflows in the last few years because they are a diversified business," he explained, "They are very solid and very transparent."