I watched every fight I could. I read every book I could get my hands on. I soaked up every interview I saw. I can still recite verbatim some of his most wonderful speeches. The hero worship I felt as a child grew stronger as I became an adult and understood more of what he had achieved. While training hard for rugby I, in my own small way, was inspired by Ali's stories about how he trained for the Rumble in the Jungle – and trained harder because of it. One of the more thrilling moments of my life was to be at the Atlanta Olympic Games opening ceremony in 1996, and recognise the frail figure about to light the torch. Muhammad!

For me, he was the complete package of everything a sportsman could be, an exemplar of physical and moral courage, of extraordinary skill mixed with a sense of fun, of generosity of spirit, of inspiration to the masses.

I grieve with billions around the world at his death. I am certain that there'll never be another like him. I have read dozens of the tributes and obituaries. But there's something crucial that is being ignored in so much of the coverage. That is, the tragedy that such a man as this, can have been so terribly damaged by his sport; that we have seen before our very eyes over the last decades, what happens when a man gets hit in the head thousands of times, and has his brain rattled against his skull and ...

And that rumbling you can hear in the near distance, is not coming from the jungle. No, it is social media bursting into flames at, firstly, the very idea that the great Muhammad Ali could have actually been enduringly hurt by being hit in the head thousands of times by George Foreman, Joe Frazier, Larry Holmes and Ken Norton. (I know, I know, crazy stuff! How could Muhammad Ali be hurt by that?) The second part of the outrage is that I should raise it now, when he is still to be buried.

Enduring: The image of Ali lighting the Olympic flame in Atlanta 1996 is one of the most iconic images in sporting history. Photo: Vince Caligiuri

Let me deal with that initial part of the outrage first.

Of course no one wants to believe it.

No one wanted to believe that JFK, the most powerful man in the world, could be shot by a loser like Lee Harvey Oswald, either. Hence the proliferation of conspiracy theories that it was done by the mafia, the Cubans, the Russians, the CIA! Anything but that.

And you mean to tell me that the most beautiful woman in the world, Princess Diana, died simply because her driver was drunk, and she wasn't wearing her seatbelt? So plebian a reason as that? NO! It must be something else. MI5! MI6! It musta been the royal family that ordered the hit! Anything but that.

And so, too, the simple notion that a man who was in the boxing ring for about three decades, and spent hundreds of hours, including training, being hit in the head by the hardest men on the planet should have had – very simply – his brain damaged, has brought us many alternative explanations. One of the most common ones before the diagnosis of Parkinson's was that he had been effectively poisoned by the pesticides at one of his training camps. Another was that his brain was actually fine in there, it was just that as the most famous man in the world, with everybody wanting his attention, he had simply receded into himself and ...

And there's the rumble in the jungle again.

Many are now screaming, "he had Parkinson's, you dickhead! It's NOTHING to do with boxing, as you can see 'cos Michael J. Fox got it too, and he never got hit in the head once!" They must get a grip. Firstly, Parkinson's and brain damage from boxing are not mutually exclusive.

In fact, the very neuroscientist who is CEO of the Michael J. Fox Foundation for Parkinson Research, Todd Sherer, said as much this week, noting, "there's pretty convincing data that head injury can increase your risk for developing the disease".

Furthermore, Dr. Samuel Goldman, of the Parkinson's Institute and Clinical Centre in Sunnyvale, California, told Stat News earlier this month: "From what I understand there's a good likelihood that his Parkinson's is a consequence of repetitive head trauma."

How many people, ever in the history of the world, got more "repetitive head trauma" than Muhammad Ali, over such a long time?

Sherer was backed by Dr John Trojanowski, a neurologist at the University of Pennsylvania, who once met Ali and said, it's "highly likely that his early-onset Parkinson's was a result of his boxing".

Either way, boxing has a real case to answer with what happened to Ali.

I refer, as I have before, to the footage provided by Sir Michael Parkinson recently, of the four occasions he interviewed Ali. In the first one, circa 1966, the great boxer was fast, clever, articulate and at his breathtakingly charismatic best. Three years later, at the height of the conflagration caused by his righteous refusal to serve in Vietnam – "no Viet Cong ever called me n--ger" – he was mostly angry, but every bit as articulate. By the late 70s, however, he was slurring his words, a shadow of the man he once was. And then the denouement ... Sir Michael interviewed him just before his last fight in 1981, by which time Ali was a shambling wreck. It was staggering that anyone could put the 39-year-old in the ring, let alone pay to see him fight, but boxing did all right. And most of us who loved him watched that fight – making us complicit in putting him in that ring.

Now to the outrage that this matter should be raised now.

Why is that? Was there a better time to talk of the dangers of AIDS, than when Rock Hudson died? A better time to highlight the dangers of overloading on painkillers and prescription drugs, than when Michael Jackson and Prince died so young? A better time to discuss the dangers of depression, than when Robin Williams and Phillip Seymour Hoffman took their lives while suffering from it? (Lifeline 13 11 14) All those were fine to discuss, and not disrespectful, but we cannot talk of the dangers of getting repeatedly hit in the head, even when we see what happened to The Greatest himself?

It is not disrespectful. I loved Ali. His legacy is multi-faceted, enduring, and on a number of fronts at once. So can it be any bad thing that, upon his tragic death, another part of that legacy is for there to be wider recognition that if even one as beautiful, charismatic, courageous and fiercely smart as him can be brought down by getting hit in the head too often, then no one is safe if they ignore the dangers of concussion? Wouldn't he, above all others, want the kids around the world that he loved so much to be aware that they must be more careful than he was in his sport – because so little was understood back then – and to look after themselves?

Let the last of the many lessons provided by Ali, be that brain health in sport is a very serious matter, and let succeeding generation of sports people of all ages look to what happened to him, and take better care of themselves. Let us offer him a final salute.

Vale, Muhammad Ali. You were a great man.

Twitter: @Peter_Fitz