A 24-year-old man had his cheekbone fractured and nose broken when he tried to stop a group of men fighting in the street.
He was assaulted at around 11.45pm on Saturday, November 1 on Stony Stratford high street.
He was later treated at Milton Keynes Hospital and has since been discharged.
PC Steven Cann said: “The victim sustained serious injuries during this incident, therefore we are determined to bring the perpetrator or perpetrators to justice.
“The High street would have been very busy at this time of night, so I would appeal to anyone with any information to contact me via the Thames Valley Police Enquiry Centre on 101.”
If you don’t want to speak directly to the police contact Crimestoppers anonymously on 0800 555 111 or online at www.crimestoppers-uk.org.
No personal details are taken, information is not traced or recorded and you will not go to court.