Two years after declaring he would ‘juice to the gills’ for the highly controversial Enhanced Games, Australian swimming star James Magnussen looks almost unrecognisable.

The former world champion has transformed his body into a hulking, shredded frame ahead of the inaugural Enhanced Games in Las Vegas, where athletes are openly allowed to use performance-enhancing drugs under medical supervision.

Magnussen, now 35, will race in the 50m and 100m freestyle events on Monday AEST in a competition already being dubbed the ‘Steroid Olympics’ by critics.

And judging by the reaction online, fans were left stunned by the dramatic physical change from the swimmer once nicknamed ‘The Missile’.

Magnussen first raised eyebrows last year when he bulked up to 114kg while attempting to break the 50m freestyle world record wearing a banned polyurethane supersuit.

At the time, the retired Olympian admitted the sheer amount of muscle made him feel like he was ‘sinking’ in the water.

Magnussen previously weighed 114 kilograms when he won silver at the London Olympics

The former Australian swimming star dropped 17 kilograms after initially focusing on muscle mass for the Enhanced Games

Now Magnussen has unveiled his shredded new physique ahead of competing at the controversial Enhanced Games in Las Vegas

Now, after changing his training and body composition, Magnussen has dropped 17kg and unveiled a much leaner, heavily sculpted physique just days before competing in Las Vegas.

In an Instagram post captioned, ‘We know you’re watching – enjoy the show’, Magnussen showed off his chiselled body as anticipation built around the event.

Fans flooded the comments section in disbelief.

‘Lesssgoo, absolutely shredded,’ one wrote.

‘Shreddy McShredderson,’ another posted.

A third added: ‘Half man, half abdominal muscle.’

Another fan joked: ‘Juiced to the absolute gills.’

The entire concept of the Enhanced Games has divided the sporting world, with organisers openly embracing the use of substances banned in mainstream elite sport.

The controversial Enhanced Games allow athletes to use testosterone, peptides, growth hormones and other banned performance enhancers

Magnussen could earn millions if he wins his events and breaks freestyle world records at the games

Magnussen said organisers needed to ‘get this perfect’ given scrutiny surrounding the controversial event’s safety concerns

Magnussen has confirmed he has been using a protocol involving testosterone and peptides under medical supervision for almost two years.

Athletes competing at the event are permitted to use substances banned by the World Anti-Doping Agency, including testosterone, human growth hormone and EPO, provided they are approved by the US Food and Drug Administration.

The Games were founded by Australian entrepreneur Aron D’Souza, who has described the project as a pathway towards ‘super humanity – humans 2.0’.

D’Souza also believes the competition could help drive a booming anti-ageing industry.

‘Performance medicine is the road to anti-ageing; it’s the route to the fountain of youth,’ he said.

‘Nothing will improve the productivity of our society more than preventing ageing.’

The financial incentives are massive.

Magnussen stands to pocket hundreds of thousands of dollars simply by winning his races, while world-record bonuses worth up to $US1million [$A1.4million] are also on offer.

The swimmer has openly admitted the money available at the Enhanced Games eclipses what he earned during his decorated professional swimming career.

‘Me being the first athlete on board, we have to get this perfect,’ Magnussen said.

‘It’s in everyone’s best interest for me, A, to swim fast, B, to prove that this process can be done safely and, C, to document that for everybody to see.’

But critics have blasted the Games as reckless and dangerous.

In a joint statement, WADA and the International Olympic Committee condemned the event as a ‘dangerous and irresponsible concept’.

‘Such substances can lead to serious long-term health consequences – even death – and encouraging athletes to use them is utterly irresponsible and immoral,’ the statement read.

The inaugural Enhanced Games will be held at a specially built arena inside Resorts World in Las Vegas, featuring swimming, athletics, weightlifting and strongman events.