That Lennox Lewis is an ageing heavyweight can no longer be ignored. It is not just the flecks of grey on his head and chest that betray the passage of time. The scales reveal he is now the heaviest world heavyweight champion, at 18st 4½lb, since the Ambling Alp, Primo Carnera, in the 1930s.

But more damning visual evidence screams the truth: two months in a training camp has not been long enough to get Lewis in anything approaching his best fighting shape after a year of inactivity. The hard body and muscle definition  he took into the ring against Mike Tyson in Memphis, for what many would say should have been the defining and concluding episode of a magnificent career, is no longer apparent.

What catches the eye is the champion's fleshy midriff and lack of conditioning, which has added to the belief within the Vitali Klitschko camp that the huge Ukrainian is capable of taking away the World Boxing Council and International Boxing Organisation belts when he challenges Lewis here at the Staples Center tonight.

"He's out of shape, it's as simple as that," says the BBC analyst and former world champion Duke McKenzie.

"They might say it's part of the plan, or that it is good to be carrying extra weight against a bigger man. But what else can they do? They can't say he's a stone overweight. Let's not forget Lennox was knocking people out when he was 17½ stone. The extra weight can't help."

There is a distinct sense of déjà vu about it all. In April 2001, an underprepared Lewis travelled to South Africa to defend his title. His camp insisted he was in great shape but he was knocked out by Hasim Rahman.

"It looks as though he hasn't got a very long memory. You would have thought he would have learned his lesson," said the South African promoter Rodney Berman.

Lewis claimed this week that he still enjoys boxing, while in almost his next breath admitting it feels more like a job nowadays than some mysterious quest for intangible glory. Motivation is a vital part of any sportsman's make-up, but when it is no longer there in the ring a fighter can find himself in dangerous and potentially painful territory.

Although Klitschko's upright style would seem tailor-made for Lewis, the champion may not realise the full implication of his lay-off until tonight.

Lewis and Emanuel Steward, his trainer, predict a knockout win inside five rounds, and question Klitschko's mental strength. The "quitter" tag that the Ukrainian acquired when he retired on his stool with a shoulder injury in his only professional defeat against Chris Byrd is not easily lost.

On paper Lewis should win. He has prospered at a higher level than Klitschko for a decade and is coming off a fine win over Tyson. But the march of time will take its toll sooner or later. He should fulfil his promise of a knockout, but an upset could be in the offing if Klitschko is still in there punching after six rounds.