Australia's pound-for-pound UFC king Alex Volkanovski has swept all before him in the octagon but his nine-year unbeaten run is almost sure to end at the hands of Islam Makhachev, according to MMA great Daniel Cormier.

The featherweight champ is trying to join a very select group of fighters to reign in two divisions when he tackles the lightweight belt holder at UFC 284 in Perth next month - and according to Cormier, he practically needs a miracle to win.

'I'm telling you, when you get into the details of this matchup, it seems a very hard match for Volkanovski to win because his skill set is almost catered for a guy like Makhachev because of Machachev's ability to stand and also his size,' the former light heavy and heavyweight champ turned commentator said.

Cormier acknowledged that the Aussie - who weighed 100kg when he played rugby league before taking up mixed martial arts - has the ability to bulk up enough to compete with the Dagestani champ, but said it won't be enough.

'That doesn't matter. He's still shorter,' Cormier explained.

'Because he's shorter it makes [it easy] for Makhachev to use leverage against Volkanovski. I believe this would be the biggest upset in mixed martial arts history.

'Now some people will say I say that because of who Makhachev is and our friendship ... [Volkanovski] is the number one pound-for-pound fighter in the world, so some may ask why we'd consider it an upset.

'But I think it's all in the match-up and all in the guy he's fighting ... Unfortunately the guy in front of him is the number two pound-for-pound fighter in the world and many believe is number one.'

The Australian has already posted evidence of his weight gain for the fight on social media, including a photo of him looking bulked-up with the caption, 'Yo Islam... your belt's got my name on it and my knee's got your face on it!!!'

'Islam's strong,' Volkanovski said on his YouTube channel. 'Islam's going to be ready. But I guarantee you, mark my words, I'm going to be ready. I'm going to be more than ready.'

Unlike Cormier, lightweight star Michael Chandler believes Volkanovski can pull off an upset in Perth thanks to his strength.

'I'm a huge Volkanovski fan,' Chandler said. 'He's very, very good. Is he gonna be smaller than Islam? Yes, very much so. I do think Volkanovski is gonna do better than we all think he does.

'He used to weigh 210 pounds, 220 pounds, whatever he was when he was playing rugby. Your body remembers that. 

'You carry that strength with you. You carry that power with you. You carry just the hip strength of Islam not being able to take him down.

'In the striking department, Volkanovski is better than him. I think in the speed and the power department, Volkanovski is better than him.'