If a week is a long time in politics, it can occasionally seem like a lifetime in the maelstrom of track and field athletics at its highest level. Just ask Sonia O'Sullivan.

Before making the relatively short journey to Crystal Palace last Saturday, she was entitled to believe that her Olympic preparations were precisely on schedule after a superb training session at Kingston.

A week and one disillusioning race later, she goes back on track for this evening's Weltklasse at Zurich with her Sydney plans in some disarray and her self-belief in urgent need of restoration.

Those are the wages of a vastly disappointing 5,000 metres in London where she finished some 200 metres behind the Ethiopian, Ayelech Worku, after falling off the pace within a couple of laps of the start.

Worku will not be among the athletes on the start line for the 3,000 metres event at Zurich but many others with Sydney title ambitions will ensure that this is, indeed, a true test of O'Sullivan's rehabilitation.

Among them are Gabriela Szabo, the International Woman Athlete of the Year in 1999, Tegla Loroupe, the Kenyan marathon runner who finished a long way ahead of her last Saturday, and, not least, the intimidating presence of dual American champion Regina Jacobs.

The Irish woman is not the only one who has suffered in a curiously uneven season to date, a point with which Szabo's supporters will readily concur. From a situation in which she was unbeatable in major competition last summer, her form has dwindled to the point where she was upstaged by Romanian team-mate Violeta Szekely over 1,500 metres at Crystal Palace.

That followed a couple of unconvincing runs earlier in the summer and has contrived a situation in which the world champion, for the first time since making the breakthrough in senior competition, finds herself with questions to answer.

She is unlikely to conserve anything in a stadium where she has produced some great performances in the past and which now awaits her response to suggestions that a glittering career is in decline. No such doubts exist about Loroupe, an unusually talented athlete who is preparing for the Olympic marathon championship by testing her speed against some of the best middle-distance runners in the world.

Fernanda Ribeiro, the Olympic 10,000 metres champion and an old adversary of O'Sullivan, has possibly slipped past her best but the same can scarcely be said of Britain's Paula Radcliffe who performed superbly to finish within a couple of seconds of Worku last Saturday.

The one they will be watching is Jacobs, an impressive winner of the American 1,500 and 5,000 metres Olympic trials who, apparently gets stronger and quicker with the years.

Jacobs, who is thought to be concentrating on the 1,500 metres in Sydney, is now well into the final stages of her Olympic preparations and in her current form, is capable of beating anybody over 3,000 metres.

It all adds up to another searching examination of O'Sullivan's character but with her recent medical problems behind her, she was sufficiently relaxed to go on a boating trip after finishing training yesterday morning.

"This is a race in which the spotlight is likely to be on others rather than me and I'm looking forward to that," she said. "I don't feel any real pressure, other than the need to go out and prove that my run in London was too bad to be true.

"Unlike the previous week, I didn't have a particularly heavy training session on Tuesday and at this point, I feel fine."

The task awaiting Mark Carroll in the 5,000 metres is, if anything, even more intimidating. Carroll, yet to produce his old rhythm since returning from the United States, goes in a race which includes virtually all the leading contenders for Sydney.

Among them is the irrepressible Haile Gebrselassie, who, for the second time in six days, seeks to beat the world champion at the distance, Salah Hissou of Morocco. Together with Mohammed Mournit, the naturalised Belgian, and the three Kenyans, Benjamin Limo, Paul Tergat and Paul Bitok, a great race is in prospect. Sinead Delahunty goes in the women's 800 metres which, in the absence of Szabo and Jacobs, is likely to be dominated by Violeta Szekely, Kutre Dulecha of Ethiopia and the Portuguese winner of the world championship in 1997, Carla Sacremento.

The 100 metres, as ever, will provide much of the evening's drama with Maurice Greene, now restored to full fitness, set to take on Ato Boldon, his predecessor as world 200 metres champion, and Obadele Thompson.