Australia's highest finisher in the 2016 Olympic marathon, Clark said all the COVID-enforced modifications and restrictions being imposed on the rescheduled 2020 Games had prompted her withdrawal.

"I cannot get my family there, there is no athlete village, no opening or closing ceremony and no spectators - that's the Olympics for me, they are my memories of Rio," she said.

"If it cannot be like that, why would I go and run in 38-degree heat with no-one there to watch?

"The best part of Rio for me was running past my friends and family every few 'k's. I want my memory of Olympics to be the ones I have from Rio and hopefully I can build on that in Paris."

Clark, 32, who finished 18th at Rio's famous Sambodrome in 26-degrees in a time of 2:30.53, said her focus had simply shifted to the 2024 Games.

"I'm not turning my back on the Olympics, just Tokyo. I won't run well if my heart is not in it, and my heart is not in this one.

"I don't just want to make up the numbers. Someone else can have a spot and I'll work on Paris. I'm already pumped. I love racing in Europe and don't think it will be as hot as either Tokyo or Rio. Climate-wise and location-wise, Paris will be great.

"I want to put all my energy into 2024. That's only three years away now and I'm happy with the plan we've got in place for those three years, it will set me up well.

"I chatted with my coach (Philo Saunders) and he understood and is on board and my family are always really supportive. I'm better once I explain it to people and they can see that I'm fine with the decision."

Clark, who had been sitting in fourth place for Australia's three Olympic marathon spots, plans to run the Gold Coast Marathon on the first weekend in July, two years after clocking her personal best time of 2:28:08 at the event.

The Melbourne Marathon in October is also a possibility but in the meantime she will continue to train on the familiar trails around Launceston.

"I would love to do some altitude training but that's dependant on when I can travel without having to quarantine. And hopefully by the end of the year we can travel again and I can go overseas, get a fast time under my belt and Paris is still a dream."