Ex-England striker Jeff Astle died from a brain condition normally linked to boxers rather than Alzheimer's disease as previously thought, a neurosurgeon has claimed.
Dr Willie Stewart carried out a new examination of the former West Bromwich Albion forward's brain.
He said Astle, who died, aged 59, in 2002, was killed by chronic traumatic encephalopathy (CTE).
He said this had been caused by heading footballs.
Dr Stewart said CTE was formerly known as dementia pugilistica - a progressive degeneration of the the brain caused by repeated head trauma.
He said the condition was frequently mistaken for dementia, as happened to Astle when he was incorrectly diagnosed with Alzheimer's.
Dr Stewart said he believed a number of footballers could be affected by CTE.
"Jeff's case is not unique. In football there will be more and what will be happening is that this diagnosis in football may be seen as unusual," he said.
"This is the first case that we know of."
The condition can only be definitively diagnosed after death.
Mr Astle's family, who live in Derbyshire, have campaigned for the FA to carry out research into the risks of headers.
It has previously apologised for not keeping the family informed about its work.
Mr Astle's daughter Dawn said the family had always believed heading balls had caused her father's death but it had still been "shocking" to hear the results of the new tests.
"When the doctor explained he said to mum if he hadn't known he was looking at the brain of a 59-year-old man he would have thought it belonged to an 89-year-old," she added.
"That was the extent of the damage."
An FA spokesman said its rules on concussion are due to be changed ahead of the 2014/15 season.
It was initially believed Mr Astle died from Alzheimer's disease, but the coroner at his inquest ruled his brain had been damaged by heading heavy leather balls.
He played for West Bromwich Albion from 1964-1974.
He scored 137 goals in 292 league appearances for the club and is recognised as one of its greatest players.