The move means that offers are likely to be tabled during the first week of September with a result possible soon after the US Labor Day holiday on 6 September.
Meanwhile, the number of private equity companies declaring an interest in Grey increased this week when Providence Equity Partners emerged as a potential bidder.
Based in Rhode Island, Providence specialises in investing in media and communications companies. Its investments include the German communications provider Kabel Deutschland and Warner Music. It is also part of the investment group, led by Sony, that is looking to buy the Hollywood studio Metro-Goldwyn-Mayer.
The final list of suitors joining the auction for Grey is unclear. Hellman & Friedman, which is being advised by the former Young & Rubicam chairman Mike Dolan, has talked with Kolhberg Kravis Roberts & Co about a joint bid.
However, the Blackstone Group, having baulked at Grey's £800 million price tag, is not expected to proceed. Sir Martin Sorrell's WPP is currently carrying out due diligence on Grey even though the investment bank Morgan Stanley said this week it did not believe WPP would go ahead with a bid.
Similar doubts surround a possible joint bid by Havas and the private equity company Quadrangle. They follow reports that the financier Vincent Bollore has raised his stake in Havas from 5.1 per cent to 8 per cent and will press the French communications group to abandon any attempt to acquire Grey.
- Leader, p16.