At around 3am, a man in his thirties was walking along the cycle track which leads from Hob Moor to Tadcaster Road when he was approached by three men.
Two of the men grabbed hold of the victim, while the third sexually assaulted him.
The victim is understandably very distressed by his ordeal and is currently being supported by specialist police officers.
Police are appealing for anyone who was in the area of the cycle track and the allotments which are between Hob Moor and Tadcaster Road, who saw anything suspicious, or has any other information which could assist the investigation, to please come forward.
Anyone with any information is asked to contact York CID on 0845 60 60 247. Or, if you do not want to give your name, you can contact Crimestoppers anonymously on 0800 555 111.
The scene of the incident is currently sealed off to allow crime scene investigators to carry out a full examination of the area where the assault took place. This is to ensure all available evidence is gathered as soon as possible after the incident.