Microsoft is to attempt a boardroom coup at Yahoo! within a week in an effort to force the online search engine to start serious talks or accept its $41 billion (£20.6 billion) hostile bid, The Times has learnt.

It is understood that Microsoft is preparing to nominate a “slate” of executives to sit on the Yahoo! board.

Although Microsoft is not allowed to seek private understandings from its chosen executives that they would accept the software giant’s offer, in practice the executives would recommend that Yahoo! begin serious talks or accept the approach.

According to the rules that govern the way in which Yahoo! is set up, any shareholder can nominate directors before the annual meeting. The deadline for such nominations is March 14. Should Microsoft’s nominations be successful, their appointment would be effective immediately.

A banking source close to Microsoft said: “We would be negligent if we were to allow this date to pass.”

While Microsoft declined to comment, it is understood that the only event that would stop the company from launching a coup would be if Yahoo! were to begin formal, serious talks on the offer.

Microsoft is anxious to seize control of Yahoo! quickly because it is concerned about the dominance of Google, its bigger internet rival. Microsoft wants to grab a bigger share of the $40 billion online advertising market, which is set to double in two years.

In February last year, Yahoo! told Microsoft that it was not for sale but promised to devise ways for the two companies to work together to fight Google. Yahoo! is considered by Microsoft to have broken this promise and last month, Steve Ballmer, the chief executive of Microsoft, sent a letter to Jerry Yang, the co-founder of Yahoo!, offering $31 per share, up to half of which would be payable in cash. The offer - at the time valued at $45 billion – represented a 61 per cent premium to Yahoo!’s share price the day before the letter was made public.

Yahoo! has spent the month since Microsoft’s approach seeking tie-ups with other media, telecom and internet groups to protect it from the reach of the software company. It has also formally rejected the approach, declaring that the offer seriously undervalues the group.

Yahoo! approached AOL, the internet arm of Time Warner, to see if it would be interested in restarting merger talks, but AOL is understood not to have been interested. Yahoo! has also started talks with News Corporation, the parent company of The Times, over a possible joint venture that would involve merging News Corp’s MySpace social networking business into Yahoo! in return for a large shareholding. The talks are believed to be continuing.

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