The world of boxing winced yesterday as Mike Tyson said he expected Francois Botha "to die" when they meet in Las Vegas on Saturday week.

The former world heavyweight champion, during a routine press conference, suddenly launched into a tirade of obscenities against a society he said rejects his credibility, believing "the sleaziest people in the world" rather than him.

Reporters had been steered away from asking questions about Tyson's legal battle with Don King and the road traffic accident in Maryland where he admitted attacking two motorists, an offence which could see him returned to jail next month.

But Tyson's mood darkened when asked if he still felt an affinity with Sonny Liston, the former feared champion with a prison record and a mob-manipulated career who died in mysterious circumstances on December 30, 1970.

He said he did and, as he began to lash out verbally, the psychiatrist's evaluation heard when he was granted a return of his fighter's licence in October seemed apt. It read: "Mr Tyson's changes from normal mood to anger seem to be triggered by his belief that he is being used, victimised and treated unfairly."

Perhaps Tyson was merely playing the hype game when he said of Botha: "I am going right at him and I expect him to go down cold. I expect him to die." But not surprisingly the words have provoked fresh outrage.

Frank Maloney, manager of the World Boxing Council heavyweight champion Lennox Lewis, said: "Everyone knows the nature of the beast. You can't change a leopard's spots. The guy is an uncontrollable thug."

The former British and European heavyweight champion Henry Cooper said: "I can't understand why boxers persist in making these statements. Tyson is not a kid any more (he is 32) and knows that people do get killed in the ring. If it happens it only fuels the anti-boxing arguments.

"Fighters seem to think they have to say things like this to sell their contests but I don't recall Joe Louis saying anything like that."

In a sport dominated by money, the need to sell fights has led to some increasingly near-the-knuckle statements from the men who ply their trade in the ring.

Only recently, Prince Naseem Hamed claimed he was going to "send Tom Johnson to the graveyard" and there is an increasing worry that one of these macabre predictions may come true.

For Cooper, who slugged it out with the world's best in his prime, it has already gone too far.

"Money is the god now," he said. "When I went into the ring I wanted to prove I was the better fighter, not to kill someone.

"Fighters seem to think they have to make statements like these to sell their contests but I don't recall Joe Louis saying anything like that.

"There used to be a certain dignity within fighters, each pitting their skills against the other.

"Sadly, those days are long gone."

Veteran British fight figure Mickey Duff echoed Cooper's views and claimed Tyson should have his licence to fight removed. "Statements like these are detrimental to boxers and boxing and only add more weight to the anti-boxing lobby," he said.

"I had 69 professional fights and I never wanted to kill anyone. It is particularly unfortunate coming so soon after the death of Jerry Quarry. It is bad for his memory.

"People are entitled to be allowed to earn a living but sometimes they go too far."

The apparent instability within Tyson remains worrying as he approaches his first contest for 17 months since being suspended after his disqualification against Evander Holyfield for the infamous ear-biting episode. His backers, reported to be paying him $30 million (£18 million) to take on the rugged 30-year-old South African Botha, are entitled to feel twitchy.

Glenn McCrory, the former World Cruiser-weight Champion, spent two years as a Tyson sparring partner a decade ago. Where once he coped with Tyson's blows, now he tries to assess the frightening mood swings in the old champion.

"I can understand where he is coming from, because he feels the world is having a pop at him. He needs good people around him, otherwise he can't control his anger.

"Somewhere in his life he may have lost control. Mike's become his own worst enemy. It can be hard to find a purpose as a boxer: most of us understand that. It's a sport where, everything you live and strive for, others find horrendous. But it's what he loves.

"In saying he's going to kill Botha, perhaps Mike's trying to say what he thinks people want. He needs somebody to say `stop' but I don't think he respects anyone any more. Perhaps he's lost his own self-respect and peace of mind. When you've lost that, you've lost everything. Underneath I know there is a nice soft-spoken guy, but how can he become that man again?"

The revulsion at Tyson is predictable but Botha may be smiling because, where once the words would have been attributed to an overbearing monster, now they come from one who will never again be seen as an invincible intimidator. Mike Tyson is becoming an object of pity.

Former world flyweight champion Charlie Magri reacted with disgust to Tyson's words. "If you want boxing to survive, you will have to do it without Mike Tyson," said Magri.

"He was good for the game at one point but the sooner he has his licence taken away the better. Boxing is all about winning on points and knocking people out - not killing them.

"Tyson is just a bully and whenever he fights people who are not intimidated by him, he loses."

British Boxing Board of Control secretary John Morris was unable to comment of the specific statement, but said: "We have expressed grave concerns about Mr Tyson's behaviour over a sustained period of time."