Edinburgh: Queen Elizabeth II will not attend a traditional highlight of her summer trip to Scotland because of persistent health worries, British media said Friday.

The 96-year-old monarch has been dogged by problems walking and standing since last year, forcing her to cancel a series of public engagements.

Fears about a flare-up of what royal officials call "episodic mobility problems" have prevented her returning to London to appoint a new prime minister.

The queen had this weekend been expected to attend the Braemar Gathering near her remote Balmoral retreat in northeast Scotland.

A decision on her withdrawal was made for her comfort, British media reported, without quoting sources.

The event, which is always held on the first Saturday in September, is the most famous on the Highland Games circuit.

Senior royals, including the monarch, have attended the games regularly since the mid-19th century, to watch feats of strength and endurance.

Events include tossing the caber, in which kilted competitors endeavour to lift and throw a full-length log of Scots Pine.

Attendees this year -- the first since 2019 because of the coronavirus pandemic -- include the queen's eldest son and heir, Prince Charles.

The queen, who came to the throne in 1952, traditionally appoints the country's prime minister at an audience at Buckingham Palace in London.

In a change to convention, she will perform the constitutional role at Balmoral next week, instead of returning to the British capital.

Normally the handover of power is a swift affair, given the palace's location, just a short distance from parliament and government offices.

But the 1,000-mile (1,600-kilometre) round-trip to the Scottish Highlands will lengthen the process, delaying key appointments to the new government.

Boris Johnson, who resigned as Conservative party leader in July, will formally tender his resignation as prime minister to the queen Tuesday.

She will then ask the new Tory leader -- either Foreign Secretary Liz Truss or former finance minister Rishi Sunak -- to form a new government.

Truss and Sunak have been vying to succeed Johnson. The winner of the vote of Tory MPs and grassroots part members closes on Friday, with the winner due to be announced on Monday.

The next incumbent at 10 Downing Street will be the queen's 15th prime minister of her record-breaking 70-year reign.

Her first was World War II leader Winston Churchill, who returned for a second term of office in 1951 until 1955.