Els, who had to win the $1m first prize to have a chance of topping
the Order of Merit, injured his back lifting luggage out of his car on Sunday.
He had intensive treatment in the hope of recovering, but said: "I tweaked it again on the fourth and just couldn't play."
Els, runner-up in the Masters, US Open and Open this season, was level par at the time and even managed to birdie the next hole.
But then came successive bogeys on the seventh, eighth and ninth and the South African told playing partner Michael Campbell - another of the Order of Merit challengers - that he felt it best to retire.
"It was getting worse and worse," he added. "I was hoping to get through today and tomorrow because I think the inflammation would have gone down by then, but I couldn't go on like that.
"I shouldn't have helped the guy getting the stuff out of the car, but I did and I paid a price.
"I've got a lot of travelling coming up, so I've got to think about that,
even though winning the European Order of Merit would have been really nice."
Els is entered for the Johnnie Walker Classic in Thailand next week and then returns to South Africa for the Million Dollar Challenge.
