After De Grasse exit, who can stop Bolt and Van Niekerk?

'Unbeatable!' was the headline Bolt said everyone would write again on Saturday night

Andre De Grasse's withdrawal through injury has only boosted the chances of Usain Bolt and Wayde Van Niekerk stamping themselves as the headline acts of the World Athletics Championships that start in London on Friday.

Bolt's main rival out of World Championships with injury

The news that the exciting young Canadian had succumbed to a season-ending hamstring strain in training on Monday gives a very different complexion to the 100 and 200 metres, in which he was expected to offer perhaps the biggest threat to the duo.

In the 100 metres, it had appeared that De Grasse had begun to get under the skin of the usually unflappable Bolt, who is seeking to end his matchless career with a seventh global 100 metres title in Olympic and World Championships.

Not only had the 22-year-old, a triple medallist at last year's Olympics, suggested airily that Bolt might be slowing down but his team had also said the Jamaican's camp ensured he was kept out of their recent 100m race in Monaco, a suggestion they denied vehemently.

It all left Bolt saying on Tuesday that he had been "disrespected" by an athlete that he had previously praised and while he did not name De Grasse, the widespread assumption was that it was De Grasse who had incurred his wrath.

So, with the Canadian who is considered the leader of the next wave of 100 metres men now not around to torment him, who is best equipped to ruin Bolt's farewell?

On the face of it, the onus is on an absolute beginner, Christian Coleman, and two old world title-winning foes, Justin Gatlin and Yohan Blake, who have been burned far too often by Bolt already down the years.

The unknown quantity is 21-year-old U.S. college student Coleman, who's comfortably the fastest in the world this year at 9.82 seconds but who still sounds a little starry-eyed about the prospect of beating Bolt, calling the idea "crazy".

In the US Championships, he was beaten by 35-year-old Gatlin, who told Reuters that "it is back to the old Justin, like 2004".

That is when he was Olympic 100 metres champion and had yet to be given the four-year doping suspension that was to turn him into the sport's bete noire.

Yet he has lost eight out of nine times to Bolt over 100m while, similarly, Yohan Blake, second fastest in the world this year at 9.90 seconds, has lost five out of six completed races over the distance to his training partner.

The odds remain that Bolt, even after a patchy season where he has gone under 10 seconds just once, has timed his run to the championships as assuredly as ever, his 9.95 second win in Monaco a fortnight ago suggesting plenty more to come.

"Unbeatable!" was the headline Bolt said everyone would write again on Saturday night. With his only global 100m final loss being disqualification for a false start in Daegu 2011, the suspicion indeed remains that only he can beat himself.

De Grasse, who won Olympic 200m silver in Rio in 19.80 seconds, may have had a better opportunity in the longer event, which Bolt has chosen to bypass.

Yet his absence now smooths the path for world 400m record holder Van Niekerk, who is seeking the same 200m/400m double that Michael Johnson last achieved at the 1995 Gothenburg World Championships.

The half-lap event now looks increasingly likely to be another straight fight between Van Niekerk and Botswanan Isaac Makwala, who are beginning to carve out a special rivalry over both 200m and 400m.

Van Niekerk clocked 19.84 seconds in Kingston, Jamaica, in June while Makwala recorded 19.77 seconds in Madrid a month later, the two fastest times in the world this year.

Makwala, who keeps improving at the age of 30, enjoys calling himself "Badman" but it is going to take a remarkably good man to defeat either Van Niekerk or Bolt at these championships.