The monarch, 96, has episodic mobility problems and is gearing up to mark her milestone reign.
The Queen is no longer planning to attend the Epsom Derby during her Platinum Jubilee weekend.
The 96-year-old monarch is said to want to pace herself during her milestone celebrations, with her daughter the Princess Royal representing her at the racecourse instead, The Sunday Times reported.
The Derby on Saturday June 4 was to be a personal highlight for the Queen during the four days of Jubilee festivities.
The head of state, a passionate horse owner and breeder, was due to be greeted on the course with a special guard of honour including up to 40 of her past and present jockeys.
But the newspaper revealed the monarch is now “increasingly unlikely” to head to Epsom.
Buckingham Palace declined to comment, saying the Queen’s attendance at events would not be confirmed until closer to the time.
This led her to miss a number of major events this year, including the State Opening of Parliament.
She is, Contudo, expected to delight the crowds with a double appearance on the Buckingham Palace balcony – at the start of the celebrations after Trooping the Colour on Thursday, and after the Pageant parade finale on Sunday.
The monarch is also hoping to be able attend the service of thanksgiving at St Paul’s Cathedral on Friday, with her wider family including, it is expected, the Duke and Duchess of Sussex and the Duke of York.
It could be the first time Harry and Meghan have been seen alongside the Windsor clan since Megxit and since they accused an unnamed senior royal of racism during their controversial Oprah interview.
The monarch is expected to spend time at some stage with the Sussexes, who are bring their children Archie and Lilibet over from the US.
Lili celebrates her first birthday on the Saturday, but it is not yet known when she will meet her great-grandmother in person for the first time.
At the BBC’s Party At The Palace concert in front of Buckingham Palace on Saturday night, both the Prince of Wales and the Duke of Cambridge are said to be preparing to pay public tributes to the Queen during the star-studded event, which features acts including Diana Ross and Queen + Adam Lambert.
The Queen is not expected to be there, and will watch on television instead from Windsor Castle.
No domingo, thousands of people will gather across the country as more than 85,000 Big Jubilee Lunches and street parties are staged in celebration of the Queen’s record-breaking 70 year reign.
The Met Office is predicting sunny blue skies and dry weather on Saturday with temperatures hitting 20C.
But those picnicking and taking part in the spectacular Pageant parade through central London on Sunday could face more unsettled weather, with a cloudier, chillier day and some risk of showers.
In a personal message ahead of the celebrations, primeiro ministro Boris Johnson has praised the monarch’s leadership, wisdom and lifelong service.
“With the first Platinum Jubilee ever, no monarch has ever served the country so long and, mais importante, no monarch has ever served it so well,” Mr Johnson said.
“Providing leadership and wisdom, this remarkable woman has dedicated her life to serving her people and to her beloved Commonwealth.
“She has led this country through good times and bad, inspiring people to serve others and their communities to create the pride and allegiance that unites us all.”