'One-punch' father: "My sons have loved each other since they were kids."

A Northern Irish tourist charged with a one-punch attack that critically injured his brother has been granted bail on the condition he stay away from his brother after drinking.

Barry Lyttle, 33, faced court charged with recklessly causing grievous bodily harm after allegedly assaulting his brother Patrick Lyttle, 31, in Sydney on Saturday.

Police alleged the pair had been drinking in Kings Cross at about 3:00am (AEDT) when they began to argue.

Barry allegedly punched Patrick in the face, causing him to fall and hit his head on the footpath.

In Central Local Court, Barry was granted bail on the condition he surrender his passport, provide $2,000 surety and not approach his brother within 12 hours of consuming alcohol.

Barry was supported in court by his father, Oliver Lyttle, and aunt.

Barry and his father Oliver during the proceedings. Via Twitter.

Outside court, Oliver said he was grateful for the support his family had received.

“They have loved each other from when they were kids…It’s great that he [Barry] is out,” he said.

“I want to thank everybody for the way things went and for the sympathy.”

Patrick had been travelling around Australia since June and was met by his brother and father in Sydney just four days before the incident.

After the alleged assault, he was taken to St Vincent’s Hospital with critical head injuries.

He underwent emergency surgery to remove part of his skull in order to release pressure on his brain.

He remains in a critical but stable condition.

Barry cried during his court appearance on Monday and his lawyer, Chris Watson, indicated that he was devastated and wanted to spend most of his time by his brother’s bed in hospital while out on bail.

“[They] are very close and [he] is very distressed,” Mr Watson said.

Barry will reappear in court on January 20.

This is an edited version of a story that appeared on ABC News, and has been republished with full permission.