The 22-year-old who has a virus, needs to win this week's Dubai World Championship and hope the race leader, Donald, finishes outside the top nine in order to secure the Harry Vardon Trophy and US$1,500,000.
McIlroy is still waiting for news after undergoing blood tests on his arrival in the United Arab Emirates. He had not been feeling well for some time.
"I won't get the results back until later on this week," said the Northern Irishman, who reignited his chances of winning after triumphing at the Hong Kong Open on Sunday.
"I picked up a virus and my white blood cell count was very low, so the tests were to see if it's back up again.
"I'm not energy-wise where I want to be, but I took a day off yesterday and took it easy," he said on Tuesday.
"I'm going to play the pro-am today and practise and I'll probably take another day off tomorrow - maybe hit a few balls.
"I'll really try and conserve my energy and focus it all into the four tournament days.
"I'm not 100%, but I'm still able to go out and play 18 holes and try and give it my all.
"I've still got a slim chance of trying to win the 'Race to Dubai'. It's going to be a tough ask, but I'll give my best and it would be great to finish the year on a high."
