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NEW YORK -- World-record holder Haile Gebrselassie stunned the running world by announcing his retirement on Sunday after dropping out of the New York City Marathon.

The 37-year-old Ethiopian, widely considered the greatest distance runner ever, pulled out at the 16-mile mark with a right knee injury.

"I never think about to retire. But for the first time, this is the day," Gebrselassie said at a brief news conference afterward. "Let me stop and do other work after this."

He has a string of business interests in Ethiopia, including a car dealership, a cinema, real estate and a newly opened hotel. Two days before making his NYC Marathon debut, Gebrselassie spoke passionately about improving lives in his home country.

He had said his training was going well, but in a TV interview minutes before Sunday's race, Gebrselassie revealed his knee was bothering him. He had an MRI on Saturday that showed fluid and tendinitis in the joint.

"I don't want to complain anymore after this, which means it's better to stop here," he said.

Running with the large lead pack, Gebrselassie pulled up grimacing on the downhill of the Queensboro Bridge after running 16 miles in 1:19:40.

Gebrselassie set the marathon world record of 2 hours, 3 minutes, 59 seconds in Berlin in 2008. He won two Olympic gold medals in the 10,000 meters.

In an interview with The Associated Press in Addis Ababa late last month, Gebrselassie insisted he wanted to compete through at least the 2012 London Games.

"Why should I retire? Why should I say I will retire in three or four years? You retire the very moment you utter those words," he said. "I still think about doing more."

Just as one Ethiopian star was retiring, a new one was emerging. Gebre Gebremariam won Sunday's race in his marathon debut at the age of 26.

"Haile is special. Haile is king," Gebremariam said. "So even Haile's retiring, we have to learn so many things from Haile. Haile's a good guy, even in business and in athletics. So I think we have to push to run more. I'm so disappointed when I hear this one. Maybe in my country just I have to do something about this."

New York Road Runners president Mary Wittenberg said that as of Saturday, the odds were low that Gebrselassie would even start the race. She said he had his knee drained and was given cortisone.

"At that point you realize you might not have the dream finish," she said.