Rishi Sunak meeting on Northern Ireland Protocol with EU president called off
But UK Government sources confirmed Ms von der Leyen was no longer scheduled to make the journey to the UK.
Some reports suggested Downing Street had hoped she would shake hands on a revised pact while visiting, while Sky News reported that she was also scheduled to meet the King at Windsor Castle on Saturday.
The broadcaster's report said the meeting could have been interpreted as Charles "endorsing the deal" that the Prime Minister is attempting to negotiate with the European Union in order to solve Brexit-related issues.
Baroness Hoey, a Northern Irish Brexit supporter and former Labour MP, tweeted: "If true, I cannot believe that even the advisers around Rishi Sunak, who clearly don't understand Northern Ireland, could have even contemplated this.
"Would be outrageous and I believe King Charles would not have agreed to it."
UK Government sources said that, while Ms von der Leyen's trip was no longer going ahead, it would not have been improper for the King, as head of state, to have met a visiting European leader.
"It would be wrong to suggest the King would be involved in anything remotely political," a Government source told the PA news agency.
Buckingham Palace said it would not comment.
No 10 said further talks between Mr Sunak and Ms von der Leyen would occur within the coming days, without being more exact on timings.
Speculation that No 10 is preparing to confirm a deal to fix the protocol intensified on Friday after a Downing Street source said "good progress" had been made during a phone call between the Prime Minister and the president.
The pair have spoken three times in the past week, including holding face-to-face conversations on the fringes of the Munich security conference last Saturday.
Unusually, Downing Street declined to set out Mr Sunak's plans for the weekend.
With Cabinet ministers reportedly on alert for a possible conference call over the weekend and Tory MPs being ordered into Parliament on a three-line whip on Monday, Westminster has been braced for a No 10 protocol announcement.
The protocol, signed by former prime minister Boris Johnson in 2020, was designed to prevent a hard border with Ireland after Brexit by effectively keeping Northern Ireland in the European Union's single market.
But the treaty has incensed unionists due to the trade barriers it has created between Northern Ireland and the rest of the United Kingdom.
Mr Sunak had reportedly been keen to announce a deal this week but No 10 said on Friday that "intensive negotiations" with Brussels were still under way.
According to The Times, the current offer on the table would mean an overhauled protocol that would remove almost all checks and most paperwork on goods crossing the Irish Sea.
Mr Sunak has promised the House of Commons will be able to "express its view" on his fresh protocol terms, which he hopes will get the Democratic Unionist Party (DUP) to restore powersharing in Northern Ireland.