The controversial proposed eco-town development near Weston-on-the-Green would need substantial amendments in order to go forward, the Government has hinted.
But the reassurance came with the message the Government was now viewing the scheme to build 15,000 homes on the M40/A34 junction as "a strong proposal".
Campaigners against the proposed Weston Otmoor settlement say the 2,000-acre site put forward by developers Parkridge is largely farmland.
And they insist at least a quarter of the land earmarked for an eco-settlement falls within the Green Belt.
A spokesman for the Department for Communities and Local Government said the Government would not abandon its earlier promise to protect the Green Belt.
A spokesman said: "This site is a greenfield site, as set out in the consultation document, and the decision to shortlist this location was taken on that basis.
"But as we have made clear throughout, no eco-town will build housing on Green Belt land, and this includes the Weston Otmoor proposal.
"Weston Otmoor is a strong proposal but there are challenges developers need to address, as with all locations on the shortlist.
"We desperately need more homes in this country for our young families and first-time buyers - and eco-towns are a unique opportunity to provide more affordable housing where it is needed, while pioneering new green ways of living that will act as a showcase for new developments everywhere."
The three-month consultation on preliminary views on eco-town benefits and shortlisted locations ends at the end of this month.
Parkridge already controls 1,600 acres of the site, through options to buy farmland from a consortium of landowners.
It is has held talks to acquire the remaining 325 acres from the Ministry of Defence.
The Government comments leave open the option of Green Belt land within the site remaining open for recreation and park land.
Tony Henman, of the Weston Front group created to oppose the scheme, said he found the Government's comments ambivalent.
He said: "I think they are encouraging in some ways, but we cannot trust the Government.
"They seem to be making it up as they go along. When they are confronted with a problem they try to engineer their way around it.
"We estimate that between 25 and 30 per cent of the site is in the Green Belt and the rest is greenfield."