Ryan, who quit on Tuesday, is understood to have left as a result of a breakdown of personal relations with transport commissioner Bob Kiley.
Kiley appointed Ryan last year (PRWeek, 18 September 2003), but relations between the two are thought to have become increasingly strained in recent months.
Ryan told PRWeek: ‘This hasn’t been the most inspirational career move. It’s fair to say that [my] relationship with Bob Kiley was testy at best.’
A TfL spokesman would only confirm that Ryan had quit and declined to comment on relations between Ryan and Kiley, an American who is reportedly one of Britain’s highest-paid public servants.
Kiley was unavailable for comment, but the TfL spokesman added that it was ‘too soon’ to make a decision about a possible recruitment process to replace Ryan.
Ryan will go on gardening leave, the length of which has yet to be decided.
He held the title of group communications MD, a role created to lead TfL’s first comms directorate.
The position oversees around 80 comms staff and is one of seven chief officers that report direct to Kiley.
Ryan joined TfL last October from Edelman, where he was European corporate practice head.
He previously worked at Brunswick and British Aerospace.