Jay and Isaiah Stephens are charged with intentionally and recklessly causing serious injury to Assistant Commissioner Chris O'Neill at an exclusive Melbourne boys' school.

The brothers had been drinking before the alleged attack at St Kevin's College on June 15, with one accused of saying beforehand "I don't care if we end up in jail tonight".

Their lawyers failed to get the charges against the pair downgraded in Melbourne Magistrates Court on Tuesday, as Mr O'Neill revealed his ongoing physical and mental trauma.

He suffered injuries including broken ribs, and bleeding on the brain and lungs, and still had regular pain and dizziness.

In a statement read by prosecutor Neill Hutton, Mr O'Neill also said he remained hyper-vigilant, on edge and profoundly emotionally affected by the incident.

The assistant commissioner had been off duty and in plain clothes when he followed Jay and Isaiah Stephens onto the grounds of St Kevin's College after they got off a train at nearby Heyington station.

Mr O'Neill was worried they would damage property or hurt someone before finding 20-year-old Jay Stephens urinating against a tree, Mr Hutton said.

"What are you looking at you old c***?" Isaiah, aged 18 at the time, allegedly told the officer.

"Nothing mate. All good with me," Mr O'Neill said.

"You're f***ed!" the elder brother is said to have replied before both men allegedly began kicking and punching Mr O'Neill in the face, head, back and torso.

In the lead up, they were accused of being loud and abusive on a train, where one was allegedly heard saying he didn't care if they ended up in jail.

One of the brothers was also seen vomiting.

Hours earlier, the duo allegedly abused and tried to pick a fight with players at the Chadstone Tennis Club, where Jay Stephens was accused of telling a woman who started filming them to "suck my d***".

The brothers were arrested two days after the alleged attack on Mr O'Neill.

Isaiah had shaved his head in order to avoid detection and his hair was found in the bin of a Malvern East boarding house, Mr Hutton said.

Photos tendered to court showed Mr O'Neill with blood pouring down his face, as well as cuts and bruises.

The brothers are due back in court on Wednesday.

Jay remains in custody but his younger brother is on bail.

Australian Associated Press