The retired archbishop Desmond Tutu is being treated with an intensive course of anti-biotics to treat a "persistent infection".
A statement from his foundation said he would spend a second night in a Cape Town hospital.
The Desmond & Leah Tutu Legacy Foundation, named after the anti-apartheid activist and his wife, said Mr Tutu's daughter, Revd Canon Mpho Tutu, would give a further update this afternoon.
The 83-year-old was admitted to a Cape Town hospital on Tuesday. At that time Mpho Tutu said their family hoped the Nobel Peace Prize laureate would be able to return home in a "day or two".
Mr Tutu has been treated for prostate cancer for many years.
He was awarded the Nobel Peace Prize in 1984 for campaigning against apartheid.
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