Williams, 25, is believed to have been at South Melbourne's Albion Rooftop when two men had an altercation just before 2am on Sunday.

Police were called to the venue, partly owned by former Collingwood teammate Dane Swan, and spoke to a 23-year-old man with minor injuries who didn't wish to make a formal statement.

A 25-year-old man was briefly arrested before being released and handed a fine being drunk in a public place.

Williams later told investigators he intervened after his friend was headbutted and concussed, according to the Herald Sun.

The report said the 103-game veteran with the Kangaroos and Magpies suffered a cut lip and claimed he was struck first before leaving the venue straight after the incident.

It's not the first time Williams has had issues with police.

In 2014, the then-Collingwood player received a 12-month suspended sentence after a jury found him guilty of causing grievous bodily harm to a man outside a nightclub in his hometown of Albany, Western Australia.

However, Williams told the court he'd been provoked prior to breaking the man's jaw in the 2012 assault.

It is understood the Kangaroos plan to make a statement on Wednesday afternoon.

Australian Associated Press