The Princess Royal, who is recovering from a chest infection, has cancelled a trip to Africa later this month on medical advice, said Buckingham Palace.
Anne was due to fly to Botswana and Mozambique but her brother, the Duke of York, will now go instead.
A Buckingham Palace spokesman said: "The Princess Royal is still recovering from a bad chest infection. HRH's working programme for next week has therefore been scaled back, with a number of engagements cancelled.
"As a precaution, on the advice of doctors, the princess will not undertake the planned visit to Botswana and Mozambique at the end of the month. The Duke of York will now undertake this visit."
Anne has been resting privately at home this week on doctors' orders after her engagements were cancelled following medical treatment for the chest infection.
She was treated at Aberdeen Royal Infirmary on September 9 before being discharged and returning to Balmoral.
At the start of the month she joined the Queen, the Duke of Edinburgh and the Prince of Wales at the Braemar Highland Games, which are held a short distance from the Royal Family's summer retreat in Aberdeenshire.
The 66-year-old also recently spent time in Brazil at the Olympic Games as a member of the International Olympic Committee.