A young New Zealand man appears to have escaped permanent injury after he was king hit as he and his brother walked home from a Sydney club early on Saturday, his father says.

But Alex McEwen, 19, potentially faces months of rehabilitation after he suffered a a fractured skull, brain bleeding and spinal damage during the attack outside a McDonald's restaurant in Penrith.

He and his brother Lance McEwen-Henderson, 21, were standing on a one-metre high wall when they were approached by a man about 1.30am, local media reported.

The man, Corey Beard, 21, allegedly punched both brothers, knocking Alexander over the wall, causing him to hit his head and lose consciousness.

As well as the assault, Beard is charged with possession of steroids found in his home.

Alex's father Rodney McEwen was in Auckland when he heard the news.

"Initially we didn't know whether there was going to be any brain damage or not, because these head injuries can go either way," he told APNZ today.

He flew to Sydney to be with his son, who was put in an induced coma in Nepean Hospital after the attack.

He was now awake and talking and there did not appear to be any permanent damage.

"Yesterday they did a scan and the bleed in the back of his head has reduced in size so it's going in the right direction, it's looking good.

"Now he's just on a strong med for a bad headache."

Mr McEwen said his two sons had met a group of girls at the McDonald's as they made their way home.

"They were basically talking to these girls when these guys pulled up and just started going ape s*** and screaming and attacked them, basically.

"The guys sort made out as if they were trying to steal their girlfriends or something like that. It was just stupid. It was just an excuse."

Alex moved to Sydney recently to live with his older brother, who had been there for three years, and both were working in warehouses in the city.

"He's off work now and he's got no pay, he's got no money from nowhere now. He's going to be off work for possibly a couple of months at least now so he's lost I don't know how many thousands of dollars because of these mongrels," Mr McEwen said.

"It's bloody terrible. These buggers need to be dealt to, the penalties need to be stiff enough so that they think twice before they do it. It destroys families and it destroys lives."

Lance told the Seven Network the attack came after a young woman in the car park posed for a photograph with Alexander.

"I was just freaking out because you never like to see your younger brother on the ground," Lance said.

"I thought he was dead, to be honest.

"Some guy was holding his head up and I was just screaming, 'Call the ambulance, call the ambulance'."

Beard was charged with offences including recklessly inflicting grievous bodily harm to the teenager as well as assaulting his brother but was bailed when he appeared in Parramatta Local Court yesterday.

Beard's legal aid lawyer said his client had told police he was acting in self-defence.

Beard was granted conditional bail, with the magistrate saying that it was a "regrettable incident ... involving violence between young men", the Daily Telegraph reported.

The attack comes just days after Daniel Christie, 18, was punched during a night out in Kings Cross, leaving him in a coma, while his brother Peter suffered facial injuries.

It prompted New South Wales Police Minister Michael Gallacher to give his support to re-labelling of violent offences so the wording reflected the "gutlessness" of the so-called king hit.

"King hit somehow suggests there was some sort of fair fight and something to be looked upon as a significant victory," he told reporters on Friday. "There is nothing victorious in this gutless act."

There have been several such instances in New Zealand, too.

Sky TV employee Billy Dawson died after being punched once in the head outside Auckland's Spy Bar during the Rugby World Cup in 2011.

The man who punched him, Kit John Murray, was sentenced to five years' imprisonment.

Primary school teacher Tarun Asthana, 25, died after being assaulted in Auckland CBD in November.

He suffered a serious head injury when he fell onto the pavement after being punched in the face.

Naval rating officer Grenville David McFarland has been charged with his manslaughter.

- APNZ