However, Costa denied their departure was certain, and said: "We are in discussions with them. The discussions are very much about what we can do together and they are going to take some time."
According to a source close to Y&R, such talks are thought to include lucrative new contracts for the three, or the possibility of WPP seed investment in their start-up venture.
However, the source added that Murphy, Priest and Golding are likely to reject any investment offer and will press ahead with the launch of their new agency when their six-month notice periods expire in January.
So far, no clients have been linked to the start up plans, which are understood to be based around a new agency model that will include digital creativity at its heart. However, sources point to Murphy's close relationship with RKCR/Y&R's Virgin and Marks & Spencer accounts, suggesting either could be launch clients.
Such plans would fall foul of what are believed to be six-month non-complete clauses in the trio's contracts and could pitch Murphy, Priest and Golding into a legal battle with WPP similar to Sir Martin Sorrell's fight with the former Y&R European chairman, William Eccleshare, when he left the agency to join BBDO in 2005.
That case went to the High Court, but was settled out of court during an adjournment in the initial hearing.