Tim O'Toole, the managing director of London Underground, is understood to have ruled himself out of the running to replace Bob Kiley as London's Transport Commissioner.
Mr Kiley, 70, steps down at the end of this month after five years running Transport for London (TfL). Mr O'Toole, who like Mr Kiley is American, was seen as the favourite to succeed him but transport sources have said that he does not want such a high- profile role and has decided against going for the job.
This leaves two main internal candidates: finance chief Jay Walder, also an American, and buses boss Peter Hardy.
Mr Walder is understood to have had a difficult relationship with Mr Kiley in recent months and it was reported that a row between the Transport Commissioner and London Mayor Ken Livingstone, over whether Mr Walder should leave TfL, preceded Mr Kiley's decision to quit.
Mr Hardy has overseen TfL's bus strategy, which has brought about an expansion in the number of routes and a simplification of the fares structure.
Controversially, Mr Kiley will remain on TFL's payroll for three years after he steps down - earning £736,000 in consultancy fees. He will also be able to remain in the £2.1m house in Belgravia that was bought for him by TfL and where he lives rent free.
Mr O'Toole, 50, joined London Underground in 2003, coming from the Consolidated Rail Corporation in Philadelphia.
Although he had little experience of running a passenger railway, he is seen as having done a good job at London Underground.
He was given an honorary CBE in the New Year's Honours to reflect his hard work getting the Tube network running again after the 7 July bombings.Reuse content