The International Olympic Committee (IOC) will reschedule events at the 2008 Beijing Games if air pollution is a threat to athletes' health.
The UN claims Beijing's air quality will improve little before the Olympics
In October a United Nations report said pollution in the Chinese capital was more than three times the safe limit.
"If you have a risk you may have to decide to work on the rescheduling of the competition," said the Games' executive director Gilbert Felli.
Felli confirmed any decisions would be made just prior to or during the Games.
Beijing has already poured about $16bn into environmental programmes in an attempt to reduce pollution.
Scores of factories have been dismantled or moved out of the city and thousands of high-polluting taxis and buses have been taken off the road.
But with on-going construction and an estimated 1,000 new cars hitting the streets each day, the Beijing air has further deteriorated in quality.
The UN report suggested in some cases pollution is more than three times the safe limits set by the World Health Organization and that it will not improve significantly before the Games, which begin on 8 August.
The organisers have issued assurances that contingency plans are being drawn up based on the results of trials last August, when 1.3m vehicles were banned from the city's roads for four days.
Other plans include halting busy construction during the Games as well as shutting down polluting plants.
Felli said the latest figures on Beijing's air quality had been sent to the IOC.
"We have just received the numbers but we have not analysed them," he said.
"We are trying to understand with a medical commission how this type of air quality could affect the athletes.
"The Chinese reassessed this morning that they still have to finalise some of the work promised during the bid and contingency plans at the time of the Games if air quality is not as we wish."
Beijing's efforts to improve air quality include a "blue sky day" quota, referring to a targeted number of days with acceptable levels of pollution, a process dismissed by experts as unscientific.
A campaign called "guard the blue sky" will involve inspectors cracking down on dusty construction sites, uncovered trucks and outdoor kebab vendors to "guarantee the smooth achievement" of the 2007 target of 244 blue sky days.