It was a familiar scene; Killeen has suffered tumbles at each of the last two Olympics but recovered to finish in the top 10 on both occasions.
However, that luck ran out at Hadleigh Farm yesterday when the British rider crashed on the second of the seven-lap race, breaking his ankle in the process. It was a bitter moment for Killeen, who at 30 will face a tough challenge to earn a place at the next Olympic in four-year's time.
The future appears bleak for him, then, but Matt Parker, British Cycling's head of marginal gains, urged Killeen to get back to full fitness as soon as possible and insisted the sport needs its talisman.
"We haven't spoken too much about the future but Liam is still the outstanding mountain biker in the UK," he said. "He has just won the national championships again and I think the sport needs someone like Liam still riding.
"The young kids need to be racing Liam Killeen and see what the standard is and we still need him in the sport to hold that bar up high. Hopefully they can come through and challenge him for Rio but whether he goes that far I don't know. We still need the likes of Liam in our sport."
Killeen can take some solace from the fact that the podium in Saturday's women's final featured a 40-year-old in Germany's Sabine Spitz taking silver. Parker intimated the crash was all the more painful given the progress Killeen was making but insisted that London didn't necessarily need to be a the end of his Olympic career.
"In all forms of cycling you can go for a long time so as long as the will is there and the legs keep going round then I am sure he will keep going," he said. "But I think that is one for him to answer post Games. It's a nasty break of the ankle and that is just mountain biking really.
"He was determined to move through the field quickly and was travelling quickly. Really he is devastated, mainly because he wanted to give the home crowd something to cheer. He was determined to get on the charge, that is what he is renowned for."
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