Joe Kinnear's family have revealed the former Wimbledon and Newcastle manager has been living with dementia since 2015.
The 74-year-old former Republic of Ireland international spent more than a decade as a player, winning the FA Cup, two League Cups and the UEFA Cup during his time with Tottenham between 1966 and 1975.
Kinnear's wife Bonnie has confirmed her husband, who was forced to retire at the age of 30, was diagnosed with early onset vascular dementia in 2015 and his condition has since deteriorated.
In an interview with the Daily Telegraph, she said: "He started to get moody - a bit depressed. I thought, 'this isn't right'.
"Then he got aggressive in certain situations. It just wasn't Joe. It was a problem trying to get him to see somebody but we eventually got him to a doctor and he was diagnosed in 2015.
"They classed it as early onset vascular dementia and, since then, he has just deteriorated. He's in the late stage. It is heartbreaking to see how someone can change.
"He was larger than life. He loved people. He'd walk in a pub, buy everyone a drink, tell funny stories and be the life and soul of the party."
After Kinnear retired as a player, he turned his hand to management and enjoyed plenty of highs with Wimbledon before spells with Luton, Nottingham Forest and Newcastle, while his last role was in 2014 as director of football at St James' Park.
Just a year after leaving the Magpies, Kinnear was diagnosed with dementia to join a long list of footballers to have suffered with the disease. Ex-Ireland manager Jack Charlton and fellow World Cup winners Nobby Stiles, Ray Wilson and Martin Peters have all died after suffering from dementia.
Dawn Astle, the daughter of former West Brom forward Jeff Astle, has campaigned tirelessly for greater recognition of the issue since her father's death in 2002 at the age of 59 was attributed to chronic traumatic encephalopathy, a brain condition caused by repeated blows to the head.
Bobby Charlton, Denis Law, Terry McDermott and Gordon McQueen are all living with degenerative neurological conditions and Bonnie Kinnear added: "I've been greatly saddened to see so many former players battling dementia.
"It's just awful. They insure footballers against breakages, so why not against dementia? There must be enough money in football to help those who need it.
"And they must take further steps to make the game safer for those playing now and in the future. More has to be done in both areas. This is not about us - it's about the whole of football."