Craig McLachlan was forced to quit SAS Australia on Monday after admitting his body wasn't strong enough to continue with the course.

The 58-year-old actor admitted that 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.