The woman and two female friends were on a bus travelling between Dandenong Station to Bock Street in Doveton when they were bashed by a group of eight men on February 26.
The three women were repeatedly kicked and punched, according to police.
One woman suffered a “mild traumatic brain injury” and broken nose.
Victoria Police Chief Commissioner Shane Patton has described the incident as “very disturbing”.
“For something like this to happen on public transport is just horrendous,” he said.
No one has been arrested over the incident.
Police have released an image of two men they wish to speak to.
They are urging anyone who may be able to help identify the eight men to come forward with information.