Catherina McKiernan, thought to be one of Ireland's more realistic contenders for an Olympic medal in Sydney in September, announced yesterday she will miss the Games because of a back injury.

After agonising for weeks on one of the most difficult decisions of her career, the 30-year-old Cavan runner finally conceded defeat in her attempt to regain racing fitness.

"I don't feel I could be back to my very best by September and the Olympic Games are no place to be if you're not 100 per cent," she said. "I've had a back injury which has made it difficult to train consistently at the level it takes to be at my best and for an event as tough as the marathon.

"I've taken the decision at this point in order to make it possible for the Olympic Council of Ireland to select another athlete at this distance, should they chose to do so.

"I'm grateful to the OCI for having enough faith in me to select me early and I'm very disappointed that I will not be able to compete in Sydney. I look forward to returning to top competition as soon as I'm injury free and back to my best form." For the last couple weeks, however, it was apparent that all was not well in the McKiernan camp. She returned from a race in Scandinavia last month quite disillusioned after badly blistered feet had destroyed her prospects of a coveted win.

Even more ominously, it soon emerged that a recurring back injury was the source of her latest fitness troubles. Earlier, her problems were attributed to a foot injury which first surfaced in the Amsterdam Marathon in November 1998.

Chasing Tegla Loroupe's world record and a bonus of £400,000, she gave so much in getting to within two minutes of the magical time that she was always at risk of picking up an injury.

In the event, McKiernan won the race, her third victory in as many starts, to be rated the top women's marathon runner in the world that year. Success came at a heavy price, however, for it set in train a sequence of mishaps which would have demoralised a lesser athlete.

Among other things, it has kept her out of the last two London marathons which resulted in a loss of earnings. By the time she was ready to run her next marathon in Chicago last October, it was already apparent she was struggling to recover the form which made her invincible in earlier races.

After a preparation fragmented by injury problems, she admitted she was heading for the unknown when she set off for the race and it showed when she was relegated to 12th place at the finish.

This year she was forced to pull out on the eve of the international cross-country race at Mallusk because of a stress fracture of her foot which later cost her the chance of running in the London Marathon.

Victory in a 10 kilometres race in Liverpool in April was the prelude to a disappointing half marathon in Paris, a race she had previously won on a couple of occasions. At that point genuine fears were expressed for her prospects of running in Sydney.

Like Sonia O'Sullivan, she has competed in the last two Olympic Games. In Barcelona in 1992, she found the 3,000 metres event far too short for her and when she moved up to the 10,000 metres in Atlanta in 1996, the oppressive heat was a problem. Yet, in spite of the conditions, she ran with typical courage to finish 10th in the final.

Commenting on this latest setback, Ray Flynn, the national 1,500 metres record holder who now acts as her agent, said: It's unfortunate that she's had so much bad luck with injury but my hope now is that she takes the time to make a full recovery.

"In the past you always had the impression that she felt the clock was ticking for her when she set out to regain her fitness. Now I trust she gives herself sufficient time to ensure that the problem has cleared fully before she goes back running.

"Manuela Machado of Portugal was five years older than Catherina when she won the European title in Budapest two years ago, so there is no reason why she cannot return even stronger from this disappointment. As an athlete of integrity, she deserves that chance." Nowhere was the sense of disappointment more keenly felt than at the Athletics Association of Ireland where Nick Davis, the AAI president, described it as a major setback. "Given the amount of work Catherina has put in, it must a huge disappointment for her," he said. "But she is an immensely gifted athlete who has performed on this stage before and we look forward to seeing her again competing in an Ireland singlet before long."