Khan, once hailed a hero as Britain’s youngest Olympic boxing medal winner – a silver at Athens 2004 – and later lauded as a former two-weight world champion, quit, not on his stool at Madison Square Garden, but leaning on the ropes clutching his groin.

He has been hit by a definite low blow, judged accidental by the referee, some 47 seconds into the sixth round of a contest he was clearly losing, heading for the fifth defeat of his chequered career.

Instead of accepting the regulatory five minutes allowed in such circumstances Khan winced and wobbled, consulted with his corner then took little more than one minute to indicate he was not prepared to carry on. He complained he was in too much pain.

Ringside pundits and those in the BT studio lowered their eyes, shook their heads and did their best to avoid spelling out what seemed obvious to the majority in the 18,000 crowd and viewers at home that Khan, in the pugilistic parlance, had bottled it.

That he wanted out because he knew he could not win against one of the world’s greatest fighters was an understandable conclusion.

His discretion on this occasion had seemed to get the better of the customary valour he had shown in so many of his previous 37 professional contests.

No boxer should ever be deemed a coward. It takes guts and unbridled bravery even just to step into a ring. But Khan let himself and his sport down by not giving himself the statutory opportunity to recover.

In my view – and remember it was Khan not me who took the blow – he could have continued. That he elected not to do so was totally out of character. Maybe he was thinking not so much of his own future but that of his family and whether or not he should risk more than just his reputation.

In three of his four earlier defeats he had gone out on his shield after being knocked out. This time he limped to the dressing room complaining he had been hit in the testicles. Well, those King Khan crown jewels must have been in an odd place because TV replays showed Crawford’s left hook had landed on the top edge of the heavy leather protective cup that has to be worn by all boxers. It may have hurt and pinched into the groin but it did not appear that damaging.

Khan argued he "couldn’t think straight". He had been knocked down in the first round by the 31-year-old American and was behind on all three judges' scorecards when the fight ended.

“I gave my all. If I am criticised so be it,” he said. “I have never quit in any fight. I'd rather be stopped on my feet or the floor.”

That may be so. But at 32 Khan seems to have lost the nifty leg movement that was one of his trademarks. He was repeatedly off balance and inaccurate with his punches. He should retire now and listen to the sage conclusion of former world middleweight champion Andy Lee, one of BT’s pundits who said of his career: ”In terms of boxing, there are more yesterdays than tomorrows."

Yet Khan now insists he can still win another world title. He is deluding himself. At best he can pick up a decent enough purse by meeting his long-time domestic rival Kell Brook. But it is a pairing that you might say is well past its Kell-by date. It is a contest that might sell well in Sheffield but would not interest American television networks who fork out the big money only for marquee match-ups.

This time two years ago it might have been a blockbuster but not now. Though doubtless, Sky will over-hype it as one if the greatest domestic battles since the War of the Roses.

Ironically, years ago Khan might have been declared the winner over Crawford in a disqualification. But the present ‘no foul’ rule for an unintentional low blow was first introduced in America in the early 1930s after a British heavyweight named ‘Fainting’ Phil Scott has won half a dozen times on a disqualification by hoisting his trunks up to almost chest height. The last time, by coincidence, was at Madision Square Garden.

Fighters can be disqualified for many reasons, from persistent holding or hitting on the break to head butting or biting, a la Mike Tyson.

The most famous low blow disqualification in boxing history was in 1930 when the German Max Schmeling became the only boxer to win the world heavyweight title in this manner when hit low by Jack Sharkey at Yankee Stadium in New York.

While Khan ponders his future, running the gauntlet of scepticism and scorn which now clouds his career, he should not be considered anywhere near as shamed as the American heavyweight contender Jarell Miller, who failed a drugs test three times last week and is now ruled out of his title fight with Britain’s Anthony Joshua in New York on June 1.

The podgy Miller is the latest in a long line of boxers, notably heavyweights, who have resorted to doping, making it almost as endemic in the sport as it is in athletics and cycling.

It has been a gathering storm for some time and is now at a dangerous level.

Just last year Michelle Verroken, head of the advisory body Sporting Integrity, and the former head of UK Sport's Anti-Doping Unit, warned that the lack of clarity around sanctions is putting boxers' health in jeopardy and also risking a raft of legal suits being filed by fighters injured by opponents later proven to have doped.

"Instead of different standards operating from state to state, country to country, there should be one standard," she said.

"Doping in boxing is dangerous, but it’s partly because of the seriousness of additional aggression or strength that might come from using steroids. There is also the prospect that somebody has been able to retain benefits of doping substances. There is evidence showing the retention of muscle memory and strength.

"Now is the time for sanctioning to take into account the impact of residual benefits. The sanction has to be long enough so they cannot return until the benefits are gone and a level playing field resumes. If not, we’ll continue to see people using doping substances because their opponent did.

"I’m sure it won’t be long before a case is brought against someone who does take that risk with someone else’s life. The health and safety of the opponent, and not just the offending athlete, is at risk in combat sports. I’m sure there will be at some point in time a legal case where somebody wants to have their opponent charged for fighting under the influence of drugs and potentially doing them harm."

Verroken even suggested a fighter who accidentally kills a rival in the ring and is then found to have doped, could leave themselves open to a possible criminal charge.

And a death in the ring caused by a doped-up boxer would put the whole sport in jeopardy much more so than the shock surrender of a great warrior who may for once may have lost his nerve in the heat of battle.