Thabo Mbeki said he knew the ailing elder statesman's doctors and that they were doing an excellent job, the station reported.
He was speaking at a memorial lecture for former ANC president Zaccheus Mahabane on Saturday.
Mandela spent his 37th day in the Mediclinic Heart Hospital in Pretoria on Sunday. He was admitted on June 8 due to a recurring lung infection.
Last week, the presidency said Mandela was responding to treatment but was still in a critical but stable condition.
Meanwhile, visitors outside the hospital on Sunday said they were there to teach Mandela's legacy and be part of history.
Spruitview resident Vusumzi Makalima brought his four children to the hospital to teach them about Mandela.
"The kids wanted to know where Madiba was … what he did, and why he was in prison," he said.
"I wanted to teach them about what he did for the country, and show them where he was hospitalised."
He said the visit was about teaching Mandela's legacy to his children so they would not forget.
Another Johannesburg resident also visited to be a part of history.
"This will go down in the history books and I wanted to be a part of history," said Joel Mdantshe.
"Mandela will be a man in the history books that will not be forgotten."
Mdantshe and his friends posed for pictures at the shrine and said they would keep the pictures safe to remember that they visited the hospital where Mandela was.
"Even if we can't see him, we will remember that we were here, so close to him, just the building standing between us and Tata," said Mdantshe. – Sapa