'Don't know where I am': Aussie star's shock moment at national swim trials

Emily Seebohm must sweat it out until her next event on Friday after missing out on world swimming titles selection in a shock result at the national trials.

Food poisoning disrupted her preparation, but the shock miss has been even harder to stomach.

The Dolphins veteran faces an anxious wait to earn selection for next month's world titles in South Korea after suffering a 100m backstroke upset.

Seebohm revealed before she hit the pool that her quest to make an unprecedented seventh world titles team for Australia had hit a snag due to illness.

Still, it came as a surprise when the 27-year-old was a distant fourth in the 100m backstroke final on night two of the six-day selection trials in Brisbane on Monday night.

Emily Seebohm was fourth. Image: Channel 7

The former 100m world champion cut a frustrated figure after finishing more than a second behind 19-year-old training partner Minna Atherton, who clocked a personal best 59.20 seconds.

The top two in each final earn selection, providing they also finish under the nominated qualifying time.

Seebohm must now sweat it out until Friday's 200m backstroke to have another crack at making the Dolphins team for July's world titles at Gwangju.

Seebohm - a 13-year national team veteran - is aiming to become the first woman to claim three straight 200m world backstroke titles.

But she hinted that not everything had gone to plan before contesting the 100m final, after qualifying second fastest behind world junior record holder Atherton.

Emily Seebohm in action. (Photo by Chris Hyde/Getty Images)

Seebohm revealed she had struggled to recover at training after being struck down by food poisoning when contesting the FINA Champions Swim Series in Guangzhou, China in late April.

"I have had an unlucky preparation. It hasn't been smooth sailing," she told AAP.

"I am here just to see how I will go and will let these girls push me as far as I can go.

"But it (illness) is unfortunate. It changed my plans and what I was hoping to do.

"I don't really know where I am at this point. It is a bit of a gamble."

Atherton expected Seebohm - who has a staggering 53 career international medals - to bounce back in the 200m.

"She pushes me every day, it's great to train with the best in the world," Atherton said.

"We still have the 200m on Friday so we will see how she goes."