What pop star turned Aussie Olympic swimming hopeful Cody Simpson has to do as he looks to secure his spot in Dolphins squad ahead of Paris Games

Cody Simpson will swim in the heats of 100m butterflyTop two finish in final will guarantee his Olympic selectionReturned to the sport five years ago after pop stardom

Pop star turned swimmer Cody Simpson will soon discover if he is good enough to be an Olympian in Paris in what will his final sporting 'throw of the dice'.

The 27-year-old will swim in the heats of the 100m butterfly - his pet event - at the Australian trials in Brisbane from 11am AEDT, with the final on Saturday night.

Standing in his way are the likes of Matt Temple and Shaun Champion - and his coach Michael Bohl was cagey when asked if Simpson was primed for the swim of his life.

'You just don't know,' Bohl declared.

'It's a challenge, but he's as ready as he's ever going to be....this is his last throw of the dice and we're hoping he can get up and just get the best out of himself.

Pop star turned swimmer Cody Simpson will soon discover if he is good enough to be an Olympian when he competes in the heats of the 100m butterfly at the Australian trials in Brisbane

His girlfriend Emma McKeon has already booked her spot on the Dolphins team ahead of the Paris Games in July

'He's looking good, but the reality is you've got to go off rankings. He's about fourth or fifth or sixth in the 100m fly.

'For him to make this team is going to take a huge swim. It's possible, but it's expected that it's going to be a challenge for him to do. I'm not saying he's going to make it, I'm not saying he's not going to make it.'

Simpson has already endured heartbreak at the Australian trials, narrowly missing the final of the 100m freestyle after finishing 10th in the heats.

Rubbing salt into the wound was Simpson then recording his best ever time on Thursday night in the B final of the 100m freestyle.

This swim was good enough to secure a position on the Australian Olympic team for the Paris Games - but it doesn't count.

Simpson missed the 100m freestyle A final by less than two-tenths of a second.

As a result, he competed in the second tier final. He won the race after recording a personal best time of 48.67.

Simpson has already endured heartbreak at the Australian trials, narrowly missing the final of the 100m freestyle

If he had achieved that sizzling time in the A final, he would be on the Paris Olympic team as a relay swimmer in the 4x100m event.

'Swimming is tricky,' Simpson told a scrum of reporters after tumbling out of contention for a 100m freestyle relay spot.

'You are training for a long time for really marginal gains, microscopic sometimes.

'I have just been banging at the brick wall trying to get to that next level, and the faster you get, the harder it is to keep getting faster.'