But spokesman Margaritis Schinas did confirm that "work is continuing" to resolve differences between London and Madrid over Gibraltar, the tiny territory at the tip of the Iberian Peninsula that was ceded to Britain in 1713 but is still claimed by Spain.
Her remarks appeared mainly aimed at Spain, which has raised concerns about the treatment of Gibraltar in the proposed text, and France, which is leading calls for improved access to British fishing waters.
"The part that is agreed is the withdrawal agreement, which is essentially how we technically leave".
Sánchez's demands will likely cause more headaches for European Union officials ahead of Sunday's EU-27 meeting, but this could not lead the deal to a breakdown, as the Withdrawal Agreement could still be approved by a qualified majority.
But Borrell rejected this idea, suggesting Sunday's meeting should not take place if the issue were not resolved beforehand.
The EU and Britain on Thursday agreed a draft declaration laying out plans for "ambitious, broad, deep and flexible" relations after Brexit, setting the stage for the divorce to be finalised at a weekend summit.
The status of the territory is disputed by Spain.
Downing Street has repeatedly made clear that agreement is needed on the future framework - setting out aspirations in areas like trade and security co-operation and believed to run to a few dozen pages - in order to press ahead with the legally-binding withdrawal agreement.
Diplomats have suggested that they could add a suitable annex to the draft deal, but they want to avoid re-opening the deal to additional demands from other countries, El País adds.
The European Commission's vice-president, Valdis Dombrovskis, said a final agreement would have to be reached on Friday to be ready for the Sunday summit.
"Until it is clear ... we will not be able to give our agreement", he warned.
She was then expected to address the House of Commons, in a statement focused on progress in European Union negotiations, at around 3:00 pm (1500 GMT), parliamentary officials said.
Merkel said Thursday at a Berlin conference of Germany's main employers' organization that "Britain's withdrawal is shaping up to be more hard than a fictitious withdrawal of another member country", simply because of the complexity of regulating the border between European Union member Ireland and the U.K.'s Northern Ireland.
May is already struggling with euroskeptics within her own party, who see the deal as a non-starter for giving too much power to the EU.