The 31-year-old man was among fans from London who tried to board their bus to escape violence at the bout on Saturday night.
He was knocked down and pulled clear by his friends, who carried him on to the coach for safety, said an ambulance spokesman.
Paramedics trying to save the man were surrounded by an angry mob and trapped on the coach by a man brandishing a chain.
A brawl had started inside the foyer at Oldham Sports Centre shortly after the end of the top-of-the-bill middleweight title fight between Jason Matthews of east London and Paul Jones of Sheffield.
A sell-out crowd of about 1,000 spectators saw Matthews win after Jones was disqualified in the seventh for continuous holding.
Witnesses said many fans had been drinking and the fighting quickly spread outside. Police said the London fans were attacked as they returned to their bus. When the two paramedics arrived to help the injured man, supporters followed them on to the coach and they found themselves trapped between rival gangs.
"The paramedics tried to resuscitate him but were surrounded and the coach came under attack with people smashing the windows from outside," said Clive Heather, the operational manager for Greater Manchester Ambulance Service. "Then a man got on to the coach swinging a chain to get to the supporters from London. He pushed the paramedics and tried to get them out of the way. It was very, very frightening."
The ambulance crew, who did not want to be named, were unable to leave the coach until police restored order.
One of the men, a father-of-two with 15 years' experience, said: "It was a baying mob. Things just got out of hand and tempers started to fly."
His colleague added: "It was raw violence, not just the threat of violence, and all of a sudden we were in the middle of it." Managers at the sports centre refused to comment but the British Boxing Board of Control condemned the scenes.
"We deeply regret this tragic loss of life of a young man who had come to enjoy himself at a boxing tournament," it said in a statement.
"There had been no trouble inside the hall and the boxing that had taken place had been enjoyable and robustly supported, apart from a disappointing main event."
The Manchester boxing trainer Brian Hughes said boxing could not be held solely responsible for the actions of a small minority, but people involved in the sport still had many lessons to learn.
"It was caused by a handful of people," he said. "The rest were local fans supporting the guys on the undercard, and they were impeccably behaved.
"It all started the night before at the weigh-in where there was a lot of animosity between the two boxers.
"They've got to stop all this nastiness at weigh-ins, all these fanfares and hype when boxers are going into the ring."Reuse content