An attack by a suspected XL Bully only ended when the victim jumped into a river.
Emergency services were called to Gander Lane, Tewkesbury, at 9.40pm on Tuesday 21 July.
The victim, who suffered bites to his arms and legs, required hospital treatment.
He only managed to flee the dog by climbing a fence and jumping into a river.
Gloucestershire Constabulary said officers have reviewed CCTV footage and are appealing for witnesses to help identify the dog’s owner.
The suspect is described as white, around 5ft 7ins tall, of a stocky build, and aged in his 30s.
He was reportedly wearing a pale-coloured T-shirt and walked off in the direction of Priors Park following the incident.
A force spokesperson added: “Anyone who recognises the description of the man or has any other information which they believe to be relevant is asked to contact Gloucestershire Police by completing the following online form and quoting incident 524 of 21 July.
Information can also be submitted anonymously by contacting the independent crime-fighting charity Crimestoppers on 0800 555 111 or through their online form.
