The wife of Nelson Mandela is at the bedside of the former South African president as he gets treatment in hospital for a recurring lung infection.
Mr Mandela, 94, is reported to be breathing unaided, but a government statement said he is in a serious but stable condition.
The BBC reports he has been in hospital three times since December.
Graca Machel accompanied him to the hospital in Pretoria on Saturday.
The South African Press Association reported she had been scheduled to speak at a conference on hunger in London, but cancelled the engagement.
Mr Mandela served as president from 1994 to 1999. His last appearance in public was at the final of the FIFA World Cup in Johannesburg in 2010.
He appeared in a brief television clip on State television in April.
Mr Mandela was awarded the Nobel Peace Prize in 1993 jointly with former President FW de Klerk for ending apartheid and bringing democracy to South Africa.