Police have released a CCTV image of a man they would like to speak to following an assault in Great Linford.
On Monday morning, the victim, aged in his 30s, tried to stop a man driving a mini motor scrambler bike outside a primary school in St Leger Drive.
The biker then drove into the victim, causing him to break his collarbone.
The offender pulled a knife from his waist band, before riding away on the bike in the direction of Gibbwin. The victim required hospital treatment, but has since been discharged.
It happened at around 8.30am.
Investigating officer PC Jonathan Legge, based at Milton Keynes police station, said: “I am releasing this image as I believe that the man pictured may have important information that can aid my investigation.
“I am appealing to anybody who was in the area at the time of the offence who believes that they may have any information, or recognises the man in this image, to contact the 24-hour non-emergency number 101, quoting reference number 43190310150, or to make a report online.
“Alternatively, you can call the independent charity Crimestoppers anonymously on 0800 555 111