Police said the man, 22, was stabbed in the stomach when he went to the aid of a stranger who was being assaulted in Police Lane.

Detective Senior Constable Jeff Highthorn said a Ballarat man, 20, was eating a tray of chips and gravy in Police Lane when a woman stole his wallet about 2.30am.

The man chased the woman, but was confronted by two male friends of the woman.

Det Sen Const Highthorn said the pair punched the man in the face, knocking him to the ground.

The Batesford man and others, who were inside the nearby Gravy Spot, then confronted the attackers in an attempt to help the victim.

One of the men then produced a knife and stabbed the Batesford man once in the stomach.

Det Sen Const Highthorn said the man was taken to Ballarat Health Services Base Hospital with a single stab wound, about 2-3cm wide, to the stomach.

He is now in stable condition.

The victim of the initial assault received cuts and bruising to his face.

The knife is believed to have been a pocket knife with a 10-12cm blade.

Det Sen Const Highthorn said police cordoned off the area this morning and had viewed CCTV footage.

Police investigations are continuing.

More to come.