The 27-year-old is chasing his third consecutive European money-list title but recognises that Swedes Henrik Stenson and Alex Noren and Danny Willett of England are in a better position.
McIlroy is fourth on the list and needs to triumph in Dubai with Stenson finishing outside the top 45, Willett failing to make the top five and Noren the top two.
"Mathematically, I can win but it's not going to happen, I wouldn't hold my breath," the Northern Irishman told reporters on Tuesday.
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"I think the three guys that are ahead of me are playing very good golf especially Henrik and Alex. I don't expect those guys to play badly this week so I'm just concentrating on trying to win the golf tournament."
A more realistic goal for McIlroy is to jump from second to first in the world rankings, displacing Australian Jason Day at the top.
"I know if I win this tournament I'll finish the year at world number one so it's a big incentive for me," he said. "It would be nice to have that little bit of momentum going into next year."
Rory McIlroy of Northern Ireland poses with the winners trophy after the final round of the Dubai Desert Classic (Reuters)
Image credit: Reuters
McIlroy has a good record in the European Tour's season-ending event with two wins and only one finish outside the top 10 in seven visits.
"It's always good to be back here," he said. "It doesn't seem like seven years ago we played our first one here in 2009.
"I have great memories from this place. Last year I had a great battle with Andy Sullivan and was able to come out on top so I'm looking forward to the week.
"I feel like my game is in pretty good shape. I've played this course pretty well in the past and hopefully can play it just as well, if not better, this week," McIlroy said.
The $8 million Dubai tournament starts on Thursday.
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