The assault took place between 23:00 on Wednesday and 00:30 yesterday morning on Green Lane, when the unknown men approached the victim from behind.
Paramedics from the Isle of Wight Ambulance Service were called to the scene alongside Police and the 20-year-old was taken to hospital for treatment after he was temporarily knocked unconscious.
The suspects have been described as all white, in their late teens and of medium build. All three are said to be under 6ft tall, wearing tracksuit bottoms and hoodies with the hoods up.
Anyone with information are asked to contact Newport police station by phoning 101. Information can be given anonymously via Crimestoppers on 0800 555 111.