Police are appealing for information following an assault in Grangefield Park, Stockton, close to the entrance with Grangefield Road.
The incident took place between 9pm and 9.30pm on Monday 20th January.
The 21-year-old man was punched in the face, leaving him with serious facial injuries which required treatment at the University Hospital of North Tees, and he will require continued medical support due to the injuries.
The suspect is believed to have been part of a group of local youths who were gathered in the park. He is described as a white male, aged 17-19 years old, of medium build, between 5ft 3” tall and 5ft 5” tall, with short, dark brown hair and he spoke with a local accent. He was wearing a blue jacket with a white stripe across the chest.
Police are keen to speak with those members of the group who intervened and prevented further injury being caused.
It is believed that a man who was walking a cocker spaniel dog may have walked past the group in the park shortly before the incident and he may be able to assist with enquiries.
Police would ask this man to get in touch.
Anyone with information regarding the incident is asked to contact DC Lee Johnson from Stockton Police Office on the non-emergency 101 number, or Crimestoppers anonymously on 0800 555 111.