About 5,000 council-owned buildings used by voluntary and community groups are likely to be sold before charities and voluntary organisations gain the legal right to bid for them, according to the umbrella body Community Matters.
The organisation, which represents neighbourhood groups, says it understands that the 5,000 community assets in England will be sold by councils between May and December this year.
A Community Matters spokeswoman said provisions in the Localism Bill, which would give charities and community groups the right to bid for these assets, are unlikely to come into force in this time. She said that the figure was "very worrying".
Hammersmith & Fulham Council in west London is one council planning to sell community assets. A spokesman said officers had produced a report recommending the sale of nine council-owned buildings, seven of which are currently used by community groups. Councillors will vote on the proposal on 7 February.
The Local Government Association declined to comment on the figures and the Communities and Local Government department was unable to comment.