Zhang Lin's London Olympics bid hangs by a thread after the 800 metre freestyle world record holder's poor performances at China's national championships, state media said Monday. Zhang finished 10th in the 200m and sixth in the 1,500m freestyle at the event in east China. He was fourth in the 400m -- a yawning 6.83sec behind winner Sun Yang. He said he was bewildered by his dismal timings, according to the official China Daily newspaper. "I am really tired and the results here are so disappointing.... I don't know what's wrong with my performance. It was supposed to be much better. I've regained my rhythm and done tests well in training," he was quoted as saying. Zhang's coach Chen Yinghong also expressed shock, blaming asthma for hindering his performances. "I was struck by the results. I think the asthma he showed... was the only explanation," he said, according to the report. Zhang's timings were well off the requirements for Olympic qualification and a shadow of his performance at the 2008 Beijing Games, when he became China's first male Olympic medallist, bagging a silver in the men's 400m freestyle. A year later, he broke the 800m freestyle world record during the Rome world championships. Men's 800m freestyle is not an Olympic event. But Zhang has vowed not to give up "as long as I still hold a slice of a chance" of securing a berth at this year's London Games, the report said. Zhang can still make the team if his performances meet requirements in international competitions or at the national youth championships in June, it added. China has high hopes for 1,500m world record holder Sun Yang, who claimed four golds in the week-long national championships that ended on Sunday.