Thames Valley Police is appealing for witnesses to a robbery in Milton Keynes on Wednesday (February 22).
At around 5.40pm the victim was cycling along a Redway off H3, Monks Way near to the entrance of Bradwell Abbey, when he was approached by a group of men wearing dark clothing with their faces covered.
One man pulled out a knife. They assaulted him and stole his mountain bike.
The suspects were described as four black men all around 6ft 2ins. One man had a large build and the rest were slim. The victim, a 23-year-old man, was a considerable way into the Redway when the group assaulted him.
The knife had a black handle and had a 9.5in blade. The stolen bike is described as a blue, silver and grey Mountain Back adult bike.
Fortunately the victim was not injured during this incident.
Anyone with information is asked to contact Detective Constable Katrina Walmsley of Milton Keynes CID via the Thames Valley Police Enquiry Centre on 101.