In his first interview since his diagnosis was made public last week, he said he was in no doubt that the heavy leather balls he played with are responsible.

       Denis said: "What else would it be? That was what caused damage to the brain. You were heading the ball, which was quite heavy in those days, but you didn't think about it. We just thought it was normal.

       "Now as time goes on, you are thinking, 'Why should I be having this problem?' People realise that if you head the ball even today that there are risks. There needs to be more research."

       Denis stopped doing it in training towards the end of his career. He added: "I no longer wanted to... when I wasn't playing in games. It wasn't nice, particularly when it was wet and it was quite sore."

       The 1964 Ballon d'Or winner has been flooded with messages of support from some of the game's greats, including Sir Alex Ferguson. And he revealed he has known for five years that something was not right.

       Denis, who has Alzheimer's and vascular dementia, said: "I hadn't been going out and I hadn't been seeing friends. After a while you start forgetting people you know."

       Denis spoke the day after former England, Liverpool and Newcastle midfielder Terry McDermott also revealed he has dementia.