Mr Gubbay - one of the leading names in his field - described as "absurd" and "ridiculous" the ENO's proposals to reduce the number of 60 choristers and 83 orchestra members.
His outburst followed chairman Martin Smith's admission the ENO had been saved from going into receivership by a £4.2m grant from the Arts Council of England.
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An opera company is not a business like a bank, it has a heart and soul where you can't use the ethics of a boardroom
"
Raymond Gubbay
"A company in receipt of large sums of public money to run a chorus and opera should do just that so it is absolutely ridiculous to make these cuts," Mr Gubbay told BBC News Online.
He added if jobs had to go then they could and should be lost from the management.
"Given the sums involved, the core should be kept together and the layers of management that have built up over the years should be stripped away," he said.
"The chorus and orchestra are the jewels in the crown of the ENO. They are the core with years of experience."
'Heart and soul'
On Tuesday, Mr Smith said the cash injection announced last week had saved the prestigious touring company from "extinction".
He admitted some of the money would be used to fund redundancies.
But he also said no decision had been made on the number of job cuts facing the company.
Mr Gubbay said Mr Smith was attempting to run the ENO like an office.
"An opera company is not a business like a bank. This is a business with a heart and soul where you can't use the ethics of a boardroom," he said.
"An opera cannot be made leaner. You cannot stage opera without its chorus - and it's an expensive business."
The ENO receives £13m a year subsidy from the Arts Council of England.
This is due to rise to £15m next year.
Gubbay said it was time the ENO opened its finances up to public scrutiny, after years of the company falling in and out of financial difficulty.
The ENO's deficit was running at £2m before the grant was awarded, and was expected to rise by 2004.
The crisis is blamed on too high expectations of box office receipts and the effects of the 11 September attacks on tourism in London.