An export ban placed on the Raphael painting The Madonna of the Pinks has been extended.
The painting is thought to have been completed in Florence in about 1507-8
The extension by the Reviewing Committee on the Export of Works of Art gives extra time for campaigners to raise funds to keep the painting, worth an estimated £34.8m, in the country.
The Raphael masterpiece is owned by the Duke of Northumberland but has been on loan to the National Gallery since 1992. The Duke wants to sell the painting to the J Paul Getty Museum in Los Angeles, but can only do so once the ban is lifted.
The original export ban, which was given in January, has been extended because Culture Secretary Tessa Jowell believed the "complex issues" over compensating the owner to keep the painting in Britain had not been resolved.
The original ban runs out on 27 August.
The National Gallery has offered a compensatory amount of £21m, which they believe will be enough to keep the painting in the country.
The Heritage Lottery Fund has decided to award £11.5m to the National Gallery to help it bid to keep the Raphael in the UK.
"Once she (Ms Jowell) has decided what amounts to a compensating offer, those concerned will be given a full and fair opportunity to
respond to that decision," a spokesman from the Department of Culture, Media and Sport (DCMS) said.
"This was a once-and-for-all opportunity to keep the Madonna in Britain and strengthen a great national collection, an opportunity we felt could not be missed," the Heritage Collection Fund's chair, Liz Forgan, said last month.
"Of course the Getty is a great public gallery, but America is a little more distanced for us Britons than Trafalgar Square," she said.
The National Gallery has had the painting since 1992
The gallery had originally been seeking £20m from the fund but revised its request after seeking advice on tax laws.
Funds to top up the grant have so far been raised through donations made by visitors to the gallery, as well as private donations, and a grant of £400,000 from the National Art Collections Fund (NACF).
NACF chairman Brian Allen said: "This jewel of a picture is now within the National Gallery's reach, and we really hope that the gallery's matching offer is accepted."
The painting is considered to be one of the most cherished small images of the Madonna and the Christ Child from the Italian Renaissance.
It is thought to have been completed in Florence in about 1507-8, just before Raphael left to start work in Rome.