It happened between 7pm and 7.30pm on Thursday (17/9) at the end of Newport Road at Woolstone.
The victim, a man in his sixties was walking when he was assaulted by up to five males.
He was punched to floor and sustained head and eye injuries and had to go to hospital for treatment. He has since been discharged.
The group of offenders made off towards the H7 Chaffron Way.
They are all described as white males and in their late teens or early twenties and around 5ft 6ins tall to 5ft 8 ins tall.
Investigating officer, Detective Constable Matthew Acland based at Milton Keynes police station, said: “This was an unprovoked assault and a very distressing incident for the victim, who suffered injuries in this attack.
“It was still quite busy in the area at this time and some may have dash-cam footage which may capture the incident or the offenders.
“I would also like to appeal to a potential witness, who is believed to have disturbed the offenders before they left the scene. If you know who this person was, or believe it could be you, please get in touch.
“If you see anything which could help or you have details which may be able to assist with this investigation, please contact us.
“You can do this by making a report online or calling the non-emergency number 101 and quoting the reference 43200293009.
“If you would prefer to remain 100% anonymous please contact the independent charity Crimestoppers on 0800 555 111.”