Casey Tennent, 20, was apprehended by Good Samaritans who came to the alleged victim's aid.

He faced the Melbourne Magistrates Court on Tuesday charged with seven offences, including attempted rape and sexual assault.

In documents released by the court, police allege Mr Tennent, of Coburg, dragged the 31-year-old victim off her bike while she was riding along the Upfield bike path near Anstey train station in Brunswick at 10.50pm on Sunday.

He allegedly pulled her into some nearby bushes and began assaulting her, putting his hands around her throat and pulling her head back, police claim.

Police allege the victim pleaded "Stop it, I can't breathe" and yelled "Get off me I'm pregnant".

She curled up into a ball to try and protect her stomach while he tried to pull her pants down, police allege.

At this point, a cyclist stopped and asked if she was ok.

Police said Mr Tennent took off, running north along the bike path, with the Good Samaritan chasing behind.

The passer-by was joined by three other strangers in the chase and the group caught up with the accused in an alleyway off Tinning Street.

They apprehended Mr Tennent after he punched the first man who had gone to the woman's aid.

They held Mr Tennent down until police arrived.

Police first on scene claim Mr Tennent was ranting that he had "imagined doing it and dreamed about it and decided to do it tonight".

He told investigators later that he had taken an unknown pill and had been drinking alcohol since 1.30pm.

The woman was taken to the Royal Women's Hospital. She had swelling under her eye and scratches on her fingers.

The extent of injuries to her unborn baby are unknown until further examinations are carried out, police said.

Mr Tennent's lawyer told the court on Tuesday it was his client's first time in custody.

He was further remanded to re-appear on July 29.