Cracknell joined the agency amid much fanfare barely four months ago , after a six-year stint as The Sunday Times' political editor.
He told PRWeek he was on the verge of accepting a new job, but would not be drawn on what it was.
He also declined to comment on whether it was an in-house or agency role, or even whether he was staying within PR, saying only that his brief spell at FD had opened his eyes to ‘a number of opportunities'.
FD group chief executive Charles Watson said FD-LLM was now being run by MDs Fiona Mason, Simon Elliott and co-founder Ben Lucas. He confirmed a direct replacement was not being sought.
PA sources suggested that Cracknell's move from journalism into a senior agency management position was ‘too big a job' for a first role in public relations.
Kevin Bell, Fleishman Hillard's regional president for the UK, Africa and the Middle East, said Cracknell was ‘a wonderful journalist', but the ‘wrong man for the job'. He accused FD of going for a ‘name' rather than a proven agency head.
Watson denied the agency had a ‘star culture', but accepted that its competitors would ‘have a field day' over the loss. Cracknell will stay on at the agency until the end of July.
-- Separately, FD has been brought in by the Royal Bank of Scotland as it completes its £4bn rights issue.