NHS North West London (NWL) medical director Mark Spencer said: "We do need to centralise, probably have fewer hospital sites."
The medical director of the largest commissioning cluster in the capital has said hospitals in north west London "will almost certainly" have to close.
The cluster has been tasked with saving about £1bn over four years.
Ealing Labour council Leader Julian Bell has said hospital closure plans are "unpopular with local people".
NHS NWL serves a population of 1.9 million people in eight boroughs - Brent, Ealing, Hammersmith & Fulham, Harrow, Hillingdon, Hounslow, Kensington & Chelsea and Westminster.
It currently has a budget of about £4bn a year and has been tasked with cutting about £1bn from its budget by 2014-15.