The Guardian reported this morning that WPP chief executive Sir Martin Sorrell will dismiss shareholder concern about a possible bidding war and make a play for Grey, which will make it the world's number one advertising business.
The £600m price tag is much lower than commentators have originally mentioned, with early valuations placing a price tag on Grey of around £700m.
Investors are concerned that WPP might end up in a bidding war with private equity groups, which are also interested in taking over Grey.
Among the groups identified are Providence Equity Partners and a joint bid from Hellman & Friedman and Kolhberg Kravis Roberts & Co.
The Blackstone Group has also been mentioned, but it is believed to have dropped out on issues of price.
There is still a question mark over a potential bid from French ad group Havas, after an initial flurry of activity that saw it talk to financial partners including Quadrangle and Blackstone.
Although Havas chief executive Alain de Pouzilhac says it can afford a bid, it is under pressure from investors not to make an offer. Financier Vincent Bollore recently raised his stake in Havas from 5.1% to 8% and is believed to be against a bid.
In the past few weeks, WPP has been looking over Grey's books and Sir Martin recently hit back at Morgan Stanley, which said it believed the acquisition of Grey would not help WPP achieve its long-term goals.
"It doesn't move the needle at all. Grey, in the context of WPP, is not enormous," Sir Martin said recently.
If WPP does launch a bid, it is expected to hold a £500m rights issue to fund the acquisition.
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