Authorities in Saudi Arabia, the world's biggest oil exporter, issued a statement on Tuesday reassuring Saudis about King Abdullah's health after doctors ordered rest because of a slipped disc.
A statement on the state news agency SPA said: "The king reassures everyone about his health and expresses his thanks to all those among the Saudi people who have expressed concern."
On Friday, SPA said the king, thought to be 86 or 87, was resting after suffering a slipped disc in his back.
On Saturday the government said Interior Ministry Prince Nayef would oversee the haj pilgrimage, which is taking place in Mecca this week.
Prince Nayef, thought to be about 76, was appointed second deputy prime minister in 2009 in a move which analysts said puts him in a strong position to become crown prince or king one day.
Analysts say the king's appointment of Nayef to the post could avert a power vacuum in the event of serious health problems afflicting the king and crown prince.
Crown Prince Sultan, also in his 80s, has been abroad for unspecified health treatment for much of the last two years and diplomats in Riyadh say he has not resumed full duties. He is outside the country after leaving for what was described in August as a holiday in Morocco.
Political stability in the monarchy is of global concern. The Gulf Arab state controls more than a fifth of the world's crude reserves, is a vital US ally in the region, a major holder of dollar assets and home to the biggest Arab bourse.