The King will not carry out royal engagements for up to a month as he recovers from surgery in hospital, Sky News understands.
The King underwent a procedure for an enlarged prostate on Friday at The London Clinic and remains in hospital, with the Queen telling patients he is "doing well" during a visit.
Sky's royal correspondent Laura Bundock says there will now be a "period of recuperation" for the King.
He will be available for state matters while in hospital and can attend to red boxes with government papers when he is discharged, she added.
The King had last carried out duties in private on Thursday, ahead of arriving in London from Norfolk to prepare for the procedure.
The monarch, who only acceded to the throne 16 months ago, had to cancel engagements ahead of the surgery as his doctors urged him to rest, though the exact nature of his treatment is not known.
The 75-year-old was diagnosed with the benign condition on 17 January after going for a check-up when he was experiencing symptoms.
It is understood he wanted to share the news to encourage other men to get themselves checked.
NHS England reported a boost in views of its "enlarged prostate" page on the NHS website, recording one visit every five seconds on the day the diagnosis was announced.
A Buckingham Palace spokesman previously said the King was "admitted to a London hospital for scheduled treatment".
"His Majesty would like to thank all those who have sent their good wishes over the past week and is delighted to learn that his diagnosis is having a positive impact on public health awareness," the spokesman added.
The Princess of Wales is also staying at The London Clinic having undergone abdominal surgery.
Ahead of his own treatment, the King visited Kate after her successful operation.
The King has so far spent three nights in hospital and it is not known when he is due to leave.