Current President Jacob Zuma says the ailment requires medical attention, but that Mandela was in no danger. Zuma added that Mandela had undergone a planned, undisclosed "diagnostic procedure." He wouldn't say which hospital the 93-year-old was being treated at.
Mandela "is fine and fully conscious and the doctors are satisfied with his condition, which they say is consistent with his age," Zuma said. "We are happy that he is not in any danger." Zuma said Mandela was expected to be discharged from the hospital Sunday or Monday.
Last year, Mandela was hospitalized for a few days with a respiratory infection. Earlier this year, he was in Johannesburg and the government said then that he was in good health.
Mandela, a Nobel peace laureate who spent 27 years in prison for fighting racist white rule, has officially retired and last appeared in public in July 2010. He became South Africa's first black president in 1994 and served one five-year term.
The Associated Press contributed to this story.