Dubai - World No 1 Luke Donald has become the first player to win the money-list crowns in Europe and the United States.
Rory McIlroy needed to win the Dubai World Championship to deny the Englishman the chance of topping the order of merit in Europe and the young Northern Irishman finished down the field after closing with a 71 on Sunday.
Donald had already clinched the US Tour's money-list crown in October.
McIlroy has been tired and drained after suffering with a viral infection for a couple of weeks and he said this had simply been a tournament too far at the end of a hectic schedule of playing events.
"I couldn't get anything going when I needed to. I played a nine-hole stretch, the last two on Friday and the first seven on Saturday, in five over. That's where the tournament got away from me," McIlroy told reporters after closing on 279, nine under.
The world No 2 also said he would be skipping next week's Thailand Golf Championship, the last event of the season on the Asian Tour.
"I can't wait to have a few weeks off," added McIlroy. "People telling you what to do and where to go.
"Another flight, more sleeping patterns messed up. Next week would have been a big struggle too.
"The doctor told me last night that no matter how bad I'm feeling now I'd be even worse if I played next week."
McIlroy will next be in action at the Abu Dhabi Championship from January 26-29.