Northern Ireland's world number three is due to tee off with Americans Dustin Johnson and Rickie Fowler at 02:45 GMT (10:45 local time) on Thursday.
The 26-year-old currently leads the Race to Dubai rankings with just three tournaments remaining.
"I'm not feeling great. I ate something a couple of nights ago and Tuesday wasn't good at all," he said.
"I thought I would be better Wednesday morning, but I had a piece of toast and a couple of bits of melon for breakfast and I came here and tried to hit some balls, but even just making a couple of swings my stomach was too sore.
"I just need another day of rest and hopefully I will be better tomorrow and I can play."
Four-time major winner McIlroy is the only two-time winner of the Race to Dubai - the European Tour's season-long event - having claimed titles in 2012 and 2014.
He currently leads England's Danny Willett, Irishman Shane Lowry and South African Louis Oosthuizen.

The 33ft (10m) deep hole appeared in Fontmell Close, St Albans, a former clay pit site, on 1 October last year.
Investigations into the cause mean utilities to some homes have not yet been restored and the road has not reopened.
Hertfordshire County Council hopes the work will be completed by Christmas.
More on this story and others from Hertfordshire
Following the collapse in the early hours, families in more than 50 homes were left without power, water or sanitation before temporary solutions were provided for the majority.
Residents still have to use a temporary road built across a nearby heath.
A full microgravity survey and exploratory drilling established the hole was caused by old mine workings and a ground subsidence investigation report found that no evidence "indicated further significant mined voids".
Councillor Terry Douris said: "It was essential that we established the cause of the collapse before we started repairs.
"This has been an extremely stressful time for the residents and it would be wonderful if they can be safely back in their homes for Christmas."
Ben Bagshawe was evacuated on the night along with his heavily pregnant wife, and their baby boy was born a week later.
They have been renting a flat for the past year with the cost covered by his insurance.
"It's been frustrating but not the end of the world," he said.
Rosemary and Derek Broom, the residents closest to the hole who have been able to remain in their house, said they feel the road is now "the safest place to live in the country".
"The roads, the fields, the children's play area, everything has been so well surveyed we don't feel at all worried," Mrs Broom said.

Police said the victim was set upon by up to eight men in the Heights area at about 02:00 BST on Sunday.
A 30-year-old man was arrested but has since been released on police bail pending further enquiries.
Police have appealed for information about the attack.
Rory McIlroy hopes to play in the WGC-HSBC Champions event in Shanghai despite suffering with food poisoning.
[NEXT_CONCEPT]
Four families who had to move out of their homes when a huge sinkhole opened up in their road are still waiting to return after a year.
[NEXT_CONCEPT]
A 28-year-old man has been beaten by a gang armed with metal bars and bats in Coleraine, County Londonderry.