The Queen has been advised by doctors to rest for at least the next two weeks and only undertake "light, desk-based duties", Buckingham Palace has said.
It means the 95-year-old monarch will be unable to attend the Festival of Remembrance on Saturday 13 November.
However, the palace has said Her Majesty has the "firm intention" of leading the nation in honouring the country's war dead on Remembrance Sunday the following day.
The monarch is said to remain in "good spirits" and recorded a speech for the COP26 this afternoon.
It comes after she was forced to pull out of attending the upcoming climate summit after a busy recent schedule.
The Queen had an overnight stay in hospital, her first in eight years, as she underwent tests last Wednesday.
It meant she had to cancel a two-day trip to Northern Ireland.
During outings ahead of her hospital visit, she was seen with a walking stick at a public event for the first time.
Sky's royal correspondent Rhiannon Mills said Her Majesty's hospital admission was not related to COVID-19 - and she was back at her desk doing some light work by the afternoon the next day.
Buckingham Palace said: "Following on from their recent advice that the Queen should rest for a few days, Her Majesty's doctors have advised that she should continue to rest for at least the next two weeks.
"The doctors have advised that Her Majesty can continue to undertake light, desk-based duties during this time, including some virtual audiences, but not to undertake any official visits.
"Her Majesty regrets that this means she will be unable to attend the Festival of Remembrance on Saturday, November 13.
"However, it remains The Queen's firm intention to be present for the National Service of Remembrance on Remembrance Sunday, on November 14."
On Thursday, Buckingham Palace shared footage of Her Majesty presenting David Constantine with The Queen's Gold Medal for Poetry.
In the short clip, the Queen jokes about having to speak to him via video link saying: "I'm very glad to have the chance to see you, if only mechanically this morning!"
Earlier this week, the Queen carried out her first official engagements since spending a night in hospital as she held virtual audiences at Windsor Castle.
She wore a yellow dress and her three-strand pearl necklace as she met the ambassador from the Republic of Korea, Gunn Kim and, separately, the ambassador from the Swiss Confederation, Markus Leitner.