Prof Deakin, who in 1996 produced the Deakin Report on the future of the voluntary sector in England, made his comments at the Charity Trustee Networks' first trusteeship lecture last week.
He said salaries of sector chief executives in the US "were going off the scale" and that it would be unfortunate if the trend developed here.
However, Stephen Bubb, chief executive of Acevo, said the average Acevo member's salary, taken from its annual pay survey, to be published in October, was a modest £54,000.
"You pay for a professional job," he said. "There has been too much emphasis on getting people on the cheap. The days of the gentleman amateur are over."
Deakin's speech, which was themed 'The End of Innocence', also warned charities about developing "an overdependence on celebrity" - a phenomenon he dubbed "cultural cringe".
He said that although charities needed a more visible media presence, they risked being "harpooned by the media" should the celebrity connection fail.
His comments come only weeks after some members of the Make Poverty History coalition expressed regrets about Bob Geldof's level of involvement in the cause.
Deakin told the audience that charities had to tread a fine line between learning from business and retaining their independence. "We can set our own agenda," he said. "We need to fend off commercialisation, incorporation and marginalisation."
He said the sector's new-found maturity meant it needed to assess its relationship with the Government. Although this had improved since Labour came to power in 1997, he said, the sector's delivery of state services posed greater risks.
He warned of a "stark division" between small, campaigning community groups and macro-level service-delivery organisations. Collaboration did not necessarily equal co-operation, he said.
At the event, Linda Laurance, one of the CTN's founding partners, handed over the chair of the organisation to Rodney Buse.