Sir Martin Sorrell, WPP's chief, is forcing Eccleshare to work out his contract, which stipulates that he must work a six-month notice period at Young & Rubicam and then spend six months outside of agency work. He will not be able to start his new job until May 2006.
Eccleshare has already left Y&R in preparation for his new role at BBDO.
Steve Blamer, who is due to take over as the worldwide chief executive of FCB in June, has also been made to work out the six months of his contract at WPP's Grey Global Group before being able to move.
Eccleshare was brought in to BBDO as the replacement for the network's outgoing European president, Jean-Michel Goudard, who will retire this year. He has been charged with unifying BBDO's disparate agencies across Europe, the Middle East and Africa.