GIBRALTAR reportedly faces the "existential threat" of crashing out of the single market and not being included in any transition deal between the UK and EU after Brexit.
The British government has yet to make a proposal to European Union negotiators on what status the overseas territory should have, a Spanish government source has claimed.
In its draft negotiating guidelines earlier this year, the EU said decisions affecting Gibraltar would be run past the Spanish government.
It said Gibraltar would be outside any future trade arrangement unless an agreement was reached in advance between London and Madrid over its future status.
This stipulation included any deal on a post-Brexit transition period, the Guardian reported from a source in the Spanish government, which has a long-standing territorial dispute with the UK over Gibraltar.
Gibraltar's prime minister, Fabian Picardo, has previously said a hard Brexit would pose an "existential threat" to the territory because of its economic dependency on the UK's ties to the EU's internal market.
Just four per cent of voters in Gibraltar backed Leave in the UK's 2016 referendum.
British prime minister Theresa May has previously vowed to secure a Brexit deal that "works for Gibraltar as well as the United Kingdom".
A spokesman for Gibraltar's government said it would not comment "on what unnamed Spanish sources are alleged to have said".
