The young man had stayed in a local pub, The Chapel Arms, rather than going to the game when he and another City fan suffered injuries, Jones' a serious head injury that saw him rushed to Southampton General Hospital. Another man with him had 5 stitches in an eye wound.
Hampshire Police are keen to speak to any witnesses who were in the pub or nearby between around 3.30pm and 3.45pm, particularly a man and a woman who were with a young boy who was aged approximately seven to eight years old.
Detective Inspector Dave Morgan, who is leading the investigation, said: "I would like to stress that we are not viewing this incident as football-related violence, but as an isolated incident that occurred near to a football stadium.
"We are working very closely with our police colleagues in Cardiff who are providing assistance to establish exactly what happened that led to this man suffering his injuries."
Messages of support and best wishes have flooded the messageboard and an appeal has been set up to raise money for the young man and his pregnant girlfriend.
Visit here for instructions on how to donate.
Get well soon.