The government has temporarily barred the export of a John Constable painting, in the hope of raising the £2.8m needed to keep it in the UK.
An application to take the picture, Flatford Lock from the Mill House, out of the country will now be deferred until 11 January.
The painting, thought to be from 1814, shows the River Stour near Constable's father's mill in Suffolk.
It is now considered vital to the study of his early work.
The bar, imposed by Culture Minister David Lammy, follows a recommendation by the Reviewing Committee on the Export of Works of Art and Objects of Cultural Interest run by the Museums, Libraries and Archives Council.
A council spokeswoman said specific details of the application, such as the name of the painting's potential purchaser or the country the work would be exported to, had not been made public.
Lived 1776 to 1837
One of England's greatest landscape painters
Best known for painting the area surrounding his Suffolk home
Most famous work is the Hay Wain (at London's National Gallery but currently on loan)
Another work, The Lock, was sold at Sotheby's in London in 1990 for a then-record £10.8m
The committee said the 61 x 50.8 cm (about 2ft x 1.5ft) painting, which was only attributed to the artist in 2004, was of "outstanding significance" for the study of Constable's work, and in particular the phase of open-air painting in his early career.
This phase "has long been regarded as of major importance in the emerging story of naturalism in Western landscape painting", the Department of Culture, Media and Sport said in a statement.
The work featured in the Tate Britain's 'Great Landscapes' exhibition of Constable's works between June and August.
"The painting is a unique image in Constable's work which records important features of the local landscape and the workings of the lock at Flatford which are documented in no other work by the artist.
"Flatford Lock from the Mill House has no related studies, and shows a particular corner of the landscape close to Flatford Mill and Lock that is undocumented in the rest of his work."
Anyone interested in making an offer to purchase the painting is asked to contact the committee.
The Department for Culture said the decision on the export licence application for the painting may be extended until 11 May 2007 if a "serious intention to raise funds with a view to making an offer" is expressed.