Two brothers who bashed one of Victoria's top police officers on the grounds of an elite Melbourne private school are facing up to 15 years in prison.

Key points: Jay and Isaiah Stephens pleaded guilty to assaulting off-duty policeman Assistant Commissioner Chris O'Neill

Jay and Isaiah Stephens pleaded guilty to assaulting off-duty policeman Assistant Commissioner Chris O'Neill Magistrate Peter Reardon rejected their bid to have the case heard in the state's lowest court

Magistrate Peter Reardon rejected their bid to have the case heard in the state's lowest court The court heard the older brother verbally abused Assistant Commissioner O'Neil before the attack

Jay Stephens, 20, and Isaiah Stephens, 19, were on Wednesday committed to stand trial in the County Court, where they will appear at a plea hearing in the new year, over the assault of Victoria Police Assistant Commissioner Chris O'Neill.

Jay Stephens laughed as the Magistrate denied an application for the case to be heard in a lower court.

The 20-year-old — who has been in custody for more than five months — and his younger brother have struck a deal with prosecutors, who agreed to drop a number of charges.

Jay Stephens pleaded guilty to two charges, including recklessly causing injury and criminal damage.

He was on parole at the time of the offence.

His younger brother has also pleaded guilty to one charge of recklessly causing injury.

Officer attacked while off-duty

Assistant Commissioner Chris O'Neill suffered fractured ribs, bleeding on the brain and bruising to the lungs. ( Supplied )

On June 15, Assistant Commissioner O'Neill was off-duty at Heyington Station in Melbourne's inner east when he noticed the brothers running into the grounds of St Kevin's College in Toorak.

He followed them to make sure they did not hurt anyone and found the 20-year-old urinating on a tree.

"What are you looking at, you old c***," Jay Stephens said, according to court documents.

"Nothing mate. All good with me," responded Assistant Commissioner O'Neill.

The brothers then attacked the off-duty police officer, repeatedly punching and kicking him to the head and torso.

Assistant Commissioner O'Neill suffered two fractured ribs, bleeding on the brain and bruising on the lungs.

The court heard he did not return to full duties for several months, and said in a statement that he felt uneasy and more on edge.

Two years' jail would be 'inadequate', Magistrate says

Lawyers for the two young men spent the morning trying to convince Magistrate Peter Reardon to have the case heard in Victoria's lowest court.

The maximum penalty for recklessly causing injury in the Magistrates' Court is two years, compared to 15 years in the County Court.

The court heard Assistant Commissioner Chris O'Neill felt uneasy after the attack. ( ABC News )

Matthew White, a lawyer for the 20-year-old Stephens, told the court his client was impaired by alcohol.

"His reasoning and decision-making was obviously affected as a result," Mr White said.

"This is an unsophisticated offence. It lacks any planning or premeditation."

Mr White also said Assistant Commissioner O'Neill's injuries were also at the "lower end of the scale".

Nola Karapanagiotidis, a lawyer for the 19-year-old, said the pair weren't targeting police.

"It was clearly spontaneous offending that occurred within the context of these young men drinking," she said.

"The offending has no degree of planning."

But Magistrate Reardon knocked back the application and committed the pair to stand trial in the County Court.

"These two young men were clearly out for trouble on this particular afternoon," he said.

"Trouble was going to happen, whether it was Mr O'Neill or somebody else."

He described the assault as "vicious".

"I have serious reservations about whether this court has adequate sentencing power," he said.

"Two years imprisonment would be seen as inadequate.

"Both men will be committed."