World number one Justin Henin is concerned about pollution levels at next year's Olympic Games after withdrawing from a tennis tournament in Beijing earlier this season because she suffers from asthma.

"I have had asthma for a few months now and I felt very bad in New York at the end of the tournament so I was really concerned about Beijing," the Belgian told a news conference in Madrid.

Henin said had to withdraw from the China Open in September because of her asthma.

"I had to go back and see a specialist to start other treatments but I'm feeling better now. I was pretty disappointed because I wanted to play the tournament and get used to the conditions."

The level of air pollution in Beijing and its possible effects on athletes' health has been one of the biggest issues facing organisers of next year's Olympics.

A recent report by the UN Environment Program (UNEP) highlighted concerns about air quality in the city although organisers have said conditions will be improved by the time of the Games.

Henin said that she was hopeful the conditions would improve enough to allow her to take part in the Games to defend the gold medal she won in 2004 in Athens.

"It's true that Beijing is going to be tough at the Olympic Games with the problem I have but now it seems that everything is under control which is important because the Olympic Games are a very important goal for me in 2008," she said.

Henin begins the defence of her WTA Championships title in Madrid on Tuesday with a round-robin match against 20-year-old Russian Anna Chakvetadze.

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