Marathon world record holder Haile Gebrselassie has said he could withdraw from the event at the Beijing Olympics if the city fails to reduce air pollution levels.
The 34-year-old Ethiopian, who suffers from a breathing condition that forced him to drop out of last year's London Marathon, spoke of his concern after winning the Dubai Marathon on Friday.
"When I come to Beijing, things could happen...it could be worse and that's why I am a little bit worried," he told Reuters Television in an interview.
"If things are like that (still heavily polluted) I would try to run a different distance, instead of the marathon."
Pollution in Beijing, known for its noxious smog, is a major concern for athletes and officials planning for August's Games.
Olympic chief Jacques Rogge said last year that some events might have to be rescheduled if the air quality was not good enough.
Beijing has poured 120 billion yuan ($16.55 billion) into clearing the smog, with factories closed, construction halted and cars cleared from the roads in an effort to lift the grey cloak that often shrouds the city.
Gebrselassie said he was not planning to run any more 42-km distances before Beijing, with a few shorter races on the agenda before relocating to an as-yet undecided location to prepare for the Games.
The Ethiopian, who has set 26 world records, ran the second fastest time in history in Dubai on Friday, finishing in two hours four minutes 53 seconds.
He had been chasing a $1 million prize on offer for breaking his own world record but fell 27 seconds short of the mark he set in Berlin last September.
"One pacemaker at the beginning of the race didn't do the right job," he said. "I told him several times just to slow down and he didn't do that. He didn't listen to me," said Gebrselassie.
"I said to him four or five times 'what's going on, man? Cool it' And that was the mistake...really I can say I'm lucky just to finish the race. In such a kind of race, when it's too fast at the beginning there is a possibility just to drop out."