Thames Valley Police is appealing for witnesses or information following an incident of grievous bodily harm in Bletchley.
At about 1am on Tuesday, a man was assaulted outside Asda in Bletcham Way.
As the victim, a 20 year old man, exited the store with a woman, he was approached by a man from who had got out of a vehicle parked nearby.
The man asked the victim for a lighter and then he assaulted the victim. Three or four other men then exited the same vehicle parked nearby and joined the first offender. They assaulted the victim, with one of the offenders using a bladed weapon.
During the incident the victim received cuts and bruises to his body and a stab wound to the knee which required hospital treatment.
He was taken to Milton Keynes General Hospital, where he remains.
A white iPhone 5 was also stolen.
The first offender is described as a white man around 5ft 10ins with a large build. He had a bushy ginger beard. He was wearing a khaki jacket and Adidas grey jogging bottoms. He was also wearing his hood up.
The other offenders are described as three or four men all wearing balaclavas. One of the men in the group was wearing a white and blue jacket with his hood up.
The offenders were seen in a dark coloured car, possibly an estate.
Investigating officer Serena Bellis said: “The victim of this assault had to receive hospital treatment due to the injuries sustained.
“We are urging anyone who witnessed it to please come forward. If anyone has any information that could assist with the investigation, please call the 24-hour Thames Valley Police enquiry centre on 101, quoting incident number 43170118369.”