The king, who is suffering from inflammation of the gall bladder, is undergoing medical checks, state news agency SPA said on Monday.
Saudi Arabia's benchmark index declined 0.6% after shedding as much as 2.2% during the session. Petrochemical maker Saudi Basic Industries lost 1.5% and Al Rajhi Bank was down 0.5%.
Saudi Kayan Petrochemical also slid 2.1%, after it reported a second-quarter loss.
Egypt's blue-chip index <.EGX30> traded 1% higher, ending a five-day losing streak, with top lender Commercial International bank gaining 2.6%.
Dubai's main share index closed up 0.2%, bolstered by a 2.7% rise in blue-chip developer Emaar Properties.
However, the impact of the novel coronavirus on earnings weighed on some stocks.
Emirates NBD Bank ended 1.9% down after the lender reported a 58% plunge in second-quarter profit.
Emirates REIT, a Dubai-based sharia-compliant real estate investment trust, said in a statement it was considering de-listing from Nasdaq Dubai in response to a downturn in the United Arab Emirates' real estate sector and weak equity market conditions.
The company's shares were down 4.7%.
In Abu Dhabi, the index lost 0.4%, dragged down by a 2.2% fall in the country's largest lender First Abu Dhabi Bank.
The Qatari index rose 0.6%, led by a 1.8% gain in Qatar Fuel Company and a 1.2% increase in Qatar Electricity and Water Company following an increase in first-half net profit.
By Ateeq Shariff