Northampton Borough Council leader Tony Woods said he is concerned about loss of green space and lack of community and health care facilities.
Woods recognised that the development, proposed by David Wilson Homes and Persimmon Homes, could deliver 1,000 affordable homes. However, he maintained that flood defences are "unacceptably low" and could result in major flooding every 20 years.
He insisted that transport links need to be improved and deprivation on the Kings Heath estate tackled before the Dallington Heath scheme can move forward.
The council owns a third of the 55ha site. Earl Spencer's Althorp Estate owns all of the remainder and has expressed an interest in selling its share.
But Woods said the Liberal Democrat-run council is under pressure from Whitehall to accept a large amount of growth. He questioned how it will be delivered.
A spokesman for the West Northamptonshire Development Corporation, which is responsible for determining the proposals, said: "We have a team working on the planning application and the regeneration of the northwest Northampton area."
The corporation is preparing a strategy to underpin decisions on infrastructure and sustainable development. The scheme is set to be decided next spring.