Walker, one of the industry's most high-profile financial experts, will not renew his contract when it expires in February and is likely to step down from the role by Christmas.
The former chief operating officer for Europe, the Middle East and Africa at Leo Burnett was appointed as BBDO Europe's chief financial officer in January. But his autonomy is understood to have been severely restricted by the tight financial controls imposed by the BBDO headquarters in New York.
Jim Cannon, BBDO's worldwide chief financial officer, has been following the trend for more centralised control by US companies in the wake of the Enron scandal.
"Walker came in on an understanding with Cannon that he would have a very clear autonomy to manage the finances of BBDO Europe," a network source said. "What he has discovered is that he doesn't have that power and, as a result, the job is less than he would have wished."
Walker said: "I have not been given enough space to do the job I came to do. The mandate isn't what I expected."
He will be succeeded by Klaus Wendler.