McIlroy not fully fit

Briton McIlroy picked up the illness during the HSBC Champions event in Shanghai earlier this month.

"I have been in bed most of the week with a chest infection, and it's something that I picked up on Sunday night in Shanghai," the 21-year-old said.

"I then had to fly to Singapore the next day for a company day but felt really run down. When I got off the plane back home, I went straight to the doctor, and I've been on antibiotics for a week.

"But I'm feeling much better and back to about 85 to 90 per cent."

McIlroy heads the billing at the Hong Kong Open with Ryder Cup team mate and fellow Northern Irishman Graeme McDowell, who replaced him as world number nine in the rankings this week.

"When I bumped into Rory for a first time this week, he told me not to get comfortable at number nine in the world as he was determined to get back the position," US champion McDowell told Reuters.

"But we do have a friendly rivalry myself and Rory coming both from Northern Ireland as we do.

"Then there is also a little bit of personal satisfaction in taking his number nine spot, and it's nice having him behind me for a first time in a couple of years.

"But for me to get to number nine in the world is great because it is my highest ever ranking, and it reflects a great season."

McDowell, who finished tied third at last week's Singapore Open, has the chance to close in on the European Tour's Race to Dubai leader Martin Kaymer after the German decided to skip the Hong Kong tournament.

Kaymer leads second-placed McDowell by €367,600 with two counting events left.

"Martin has not played the best the past three weeks, and while I thought he would be uncatchable, another good week will mean 'game still very much on' when we get to Dubai (World Championship) next week," said McDowell.