A visibly exhausted and worried Mandla, the eldest son of critically ill Makgatho Mandela, spent the better part of Tuesday at his father's bedside.
The 54-year-old Makgatho is Nelson Mandela's only surviving son from his first marriage to Evelyn Mase, who died earlier this year.
Mandla, 30, who is Makgatho's son from his first marriage to Ann Mosehla, visited his father in the intensive care unit at Johannesburg's Linksfield Clinic.
It was not yet known what the cause of Makgatho's illness is. The former president has also been spending time at his bedside. Makgatho's wife, Zondi, died of pneumonia in 2003.
The Mandela family on Tuesday asked for privacy over Makgatho's condition. His sister, Pumla Makaziwe Mandela, said: "I will release a statement when it is appropriate, but now I want to be with my brother and do what I can for him."
An attorney by profession, Makgatho was the company secretary at Diners Club South Africa and is now with Standard Bank.
Craig Bond, of Standard Bank's card services division, said Makgatho's legal insight had added immense value to the institution.
Both Standard Bank and Diners Club South Africa expressed their deep concern over Makgatho's condition.
Democratic Alliance leader Tony Leon echoed these sentiments, saying: "Our thoughts and prayers are with the entire Mandela family at this difficult time."