Deputy London Mayor Kit Malthouse pulled out of a planned hustings for deputy mayoral candidates on Wednesday afternoon.
Malthouse faced call to resign earlier this week following allegations that he had questioned the budget being allocated to the phone hacking investigation by the Metropolitan Police.
The Organisers of the debate, Central London Forward, told The Huffington Post UK that he had to attend a funeral.
James Cleverely - Conservative head at the London Assembly - was drafted in to replace Malthouse.
Giving evidence to the Leveson inquiry into press standards on Monday, the former Metropolitan Police commissioner Sir Paul Stephenson said Malthouse had raised concerns about the amount of money spent on Operation Weeting.
"On several occasions after Operation Weeting had started and I had returned from sick leave, the Chair of the Metropolitan Police Authority, Kit Malthouse, expressed a view that we should not be devoting this level of resources to the phone hacking inquiry as a consequence of a largely political and media- driven 'level of hysteria'," Sir Paul said.
In his written evidence to the inquiry, Sir Paul said that he had told Malthouse the Met had "little choice" but to "invest significant resources" into the investigation.
"Additionally the nature of some of the revelations of media behaviour, particularly towards vulnerable members of the public, made a reopening of the investigation inevitable, from an operational viewpoint," he added.
Labour candidate for London Mayor Ken Livingstone has called on Malthouse to resign in the wake of the claims.