Legal commentators said the late-night incident in Kings Cross showed that a one-size-fits-all approach to mandatory minimum sentences was never going to work.

Barry Lyttle, 33, has been charged with punching his brother Patrick Lyttle, 31, once in the head following an argument outside a nightclub at 3am on Saturday morning.

Barry and his 74-year-old father had arrived in Australia just three days ago to visit Patrick, who has been travelling around Australia for more than six months.

Patrick remained in a critical but stable condition on Sunday evening following delicate surgery at St Vincent's Hospital to relieve pressure on his brain.

The incident came almost a year to the day after the one-punch death of 18-year-old Daniel Christie in Kings Cross.

Daniel's father, Michael, said on Sunday that he was devastated to see "another family stricken by worry and a future tormented with what could have or should have been".

He stopped short of supporting a mandatory minimum sentence, instead urging people to take responsibility and offering his support to the Lyttle family.

"Once again a single moment of rage has a catastrophic outcome for all concerned," he said.

"I cannot begin to imagine the remorse and pain that Barry will be feeling, although I can understand what the rest of the family is going through. My family wishes that we had solution for this violence."

His comments came as a steady stream of visibly upset friends visited Patrick in hospital on Sunday. They said the brothers are extremely close and their father was too devastated to utter a word.

Daniel's death sparked debate over alcohol-fuelled violence that eventually led to mandatory minimum sentences being introduced for drunken assaults.

The threshold for proving intoxication was initially low, requiring an officer to simply determine that the offender was slurring their words or unsteady on their feet.

It was then bolstered to require a high-range blood alcohol reading of 0.15 or more, three times the legal driving limit.

Barry Lyttle was charged with recklessly causing grievous bodily harm and would have faced a minimum four years in jail, however, police said he blew a low-range reading of less than 0.079.

Superintendent Michael Fitzgerald said alcohol was not an aggravating factor and it was a "family tragedy that has happened to occur on our streets".

Greens MP John Kaye said the incident showed that a blanket approach to mandatory minimum sentences would have been totally inappropriate.

"We have courts for that reason, to determine all the unique circumstances around an incident," he said. "It would be totally inappropriate in some cases to lock someone up for four years, thinking it will solve everything."

Barry Lyttle sobbed in court on Saturday and indicated he would apply for bail on Monday.