Craig McLachlan's shocking nickname was revealed during Monday night's episode of SAS Australia before he quit the show.

After being woken up at 5am, Craig, 58, decided to quickly eat some eggs with the other stars ahead of the intense training task.

AFL Women's star Abbey Holmes then told the actor: 'Get it down, sphincter lips!'

A stunned Matthew Mitcham almost choked on his meal as he questioned: 'Sphincter lips?'

'It's what he calls himself,' Abbey explained.

Later in the episode, Craig quit SAS Australia after admitting his body wasn't strong enough to continue with the course.

He admitted while he had the mental stamina needed to go all the way, physically he was struggling.

As he attempted a gruelling challenge - which saw teams crawl through mud across rough terrain- an exhausted Craig suddenly dropped to his knees.

'I need to see the doc,' he called out.

When asked what's wrong, Craig explained: 'I feel like a hot knife through f**king butter.'

Ant Middleton then instructed Craig to stand up, before he continued to yell at him until he made a decision.

'If you can't carry on, you're gonna let the team down tomorrow on the ground,' he then told him.

Craig then responded: 'I can't let them down (fellow recruits)' before taking off his number and handing it over.

'You've done the right thing. Because tomorrow, you would be on the f**king ground like a f**king idiot, by yourself, with no one to come and pick you up,' Ant said.

Craig then told Ant that he hopes he didn't disappoint him, to which he responded: 'No, you haven't let us down. You've done amazing. 

'Absolutely amazing. Your body's f**king given up on you... That's it.'

Craig then explained: 'Psychologically, I have what it takes. I've worked too hard and faced too many challenges to just pack it in'.

'For me to take my armband off... I will have to be... Broken, you know, physically.'

The actor then admitted that he could not carry on, and handed in his armband, ending his time on the show.