The 46-year-old victim had intervened during an altercation between the offender and a woman outside the stadium about an hour before the match between Barcelona and Manchester United on 27 May 2009.
The offender threatened the victim and the men went their separate ways.
Before the match started however, the offender saw the victim again inside the stadium and without provocation, violently attacked him.
During the attack he bit off part of his ear before disappearing into the crowd.
The offender was wearing a blue Manchester United away shirt with the letters DEE and number 38 on the back.
Officers are hoping someone will recognise the man from the CCTV stills or the description of the shirt.
Detective Constable Alex Robinson from the Force Football Intelligence Unit said: "The victim had done absolutely nothing to warrant such a vicious attack and has been left permanently scarred by the assault.
"As any decent person would, he simply came to the aid of a woman who was being picked upon by this man outside the stadium but thought that was the end of the matter.
"I am very keen to find this person in order to prevent him from going to any future football matches here or abroad as he is clearly not a football supporter."