Saudi Arabia's 89-year-old King Abdullah will undergo back surgery in Riyadh at noon on Saturday, state news agency SPA reported.
The monarch "will undergo a surgical operation to treat the looseness in the conjoining cord in the upper back at noon on Saturday in the King Abdulaziz Medical City for the National Guard," said SPA.
King Abdullah was admitted to the hospital late on Friday.
It had already been announced on November 11 that the monarch would have the operation. He underwent a similar procedure in October 2011 at the same medical facility.
In November 2010, Abdullah was operated on in New York for a debilitating herniated disc complicated by a blood clot that put pressure on his spine, and he had further surgery the following month.
His advanced age combined with health problems have raised concerns about the future of Saudi Arabia, which has been ruled by the Al-Saud family since 1932.
Prince Salman, 76, the king's half brother, was named crown prince in June following the death of prince Nayef bin Abdul Aziz.