Police have charged two brothers, aged 18 and 20, over an allegedly unprovoked attack on an off-duty senior Victorian police officer near a Melbourne train station.

Key points: The brothers will appear in court on Tuesday on charges including intentionally causing serious injury

The brothers will appear in court on Tuesday on charges including intentionally causing serious injury Police say the men were asked to get off a train for vomiting and urinating

Police say the men were asked to get off a train for vomiting and urinating The victim, an assistant commissioner, suffered broken ribs and head injuries

Transit and Public Safety Command Assistant Commissioner Chris O'Neill was attacked about 5:30pm on Saturday in the grounds of St Kevin's College, near a railway station in Toorak, in the city's inner east.

He was kicked and punched in the head and chest, and taken to hospital with two broken ribs, head injuries and possible kidney damage as well as bruises and cuts.

He was released from hospital on Monday.

Assistant Commissioner Bob Hill said his colleague, who suffered bleeding around the brain, was expected to make a full recovery from the "abhorrent" attack.

The attack, which was not captured on CCTV, occurred after two brothers were removed from a Glen Waverley train by authorised transit officers, Assistant Commissioner Hill said.

"Their antisocial behaviour included vomiting and urinating in the carriage, so they were, as I understand, evicted from the train at Heyington," he said.

"That's where, unfortunately, Chris crossed paths with [the] two of them."

Police said the suspects caused a disruption on the train before the assault. ( Supplied: Victoria Police )

He said Assistant Commissioner O'Neill was off duty and did not identify himself as a police officer when he encountered the two men.

"The encounter is still a little bit vague to us," he said.

"There's been a verbal altercation and then a physical altercation between Chris and the two males."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 18 seconds 1 m 18 s Police hunt brothers who allegedly launched 'despicable' attack on off-duty policeman

Police contact suspects' family

Assistant Commissioner said the men, who had been described as drunk or drug-affected by a witness, fled immediately after the attack.

Assistant Commissioner O'Neill walked to Heyington station after the assault, where he was given medical assistance by authorised officers.

"This was a despicable act. Someone going about their private business and to be attacked like this … this behaviour is abhorrent," Assistant Commissioner Hill said.

He said the two suspects lived in metropolitan Melbourne and had links to Western Australia and the Latrobe Valley.

Police contacted the suspects' family on Monday morning.

They arrested a 20-year-old man about 2:40pm in Malvern East, and his 18-year-old brother near Chadstone Road in the same suburb about an hour later.

They were charged with intentionally causing serious injury, recklessly causing serious injury, intentionally causing injury and recklessly causing injury.

The pair are expected to appear in the Melbourne Magistrates' Court on Tuesday.

Chief Commissioner Graham Ashton visited the injured officer on Monday afternoon following his release from hospital.

Assistant Commissioner Hill said the attack should not be used to draw broader conclusions about public safety.

"We have a transport system that certainly is well-policed in the state of Victoria, and Chris O'Neill has led a capability and capacity build across that part of our workforce," he said.

Anyone with information should contact Crime Stoppers.