And the second involves cricket coach Peter Moores, who has been given the responsibility of leading England's recovery out of the abyss of a 5-0 Ashes defeat barely five years after being sacked from an ill-fated stint in the same role.

The comeback is one of those fairytale storylines in sport, and can be a brilliant, latterly step in the successful career of a player, coach or administrator. But for every Hollywood-style return to greatness, there are plenty of flops, falls and failures.

The trick is, first of all, knowing the right time to call it a day and then knowing whether it is worth coming back, with talent, age, desire, reputation, and what-you-have-to-prove among the factors which must be considered.

Phelps' example is a classic one of an athlete realising the retired life is not for them. After spending the bulk of their lives embarking on a tortuous and sacrificial training routine to reach the top, they are desperate for a break, but once they have had it they find a gaping void which can only be filled by a return to action. Sometimes they come back for financial reasons but usually it is more due to a need for adrenalin, motivation or simply for something to do.

Since bursting on to the scene with a 200 metres butterfly world title in 2001 aged 15, Phelps won those staggering 18 Olympic gold medals across Athens 2004, Beijing 2008 and London 2012, as well as 27 world titles, before a long-anticipated retirement two years ago.

But over the last few months the rumour-mill has been in overdrive that he was back in training before the worst kept secret in sport was confirmed last week, with a comeback date set for a meet in Mesa, Arizona, starting on Thursday (April 24).

Michael Phelps will resume a career which has already included 18 Olympic gold medals later this week ©Getty Images



His prospects have been played down by his team, with long-term coach Bob Bowman describing how "he's just going to test the waters a little bit and see how it goes", before adding that he  "wouldn't say it's a full-fledged comeback".

But I would not get taken in by this rhetoric. Phelps' career has been based around the Olympics more than any other and the ideal plan must be Rio 2016 and an increase on his already record-breaking medal haul.

By this point, at 31 he will be fairly ancient for a top level swimmer and comparisons are already being made with the disastrous comeback of former rival Ian Thorpe in 2011. But, while Thorpe was out of action for years before coming back, Phelps has only been out the water for 18 months or so and the swimming world has not moved on too far in his absence. So unlike Thorpe, if he gets back to the same shape he was in before his retirement, he will be fast enough to win medals again.

That is a big if, particular with the depth greater than ever, but despite the long odds my view is write Michael Phelps off at your peril.

Whatever happens, Phelps will slot into one of three groups of sporting comebacks.

In the worst case scenario he will join figures like Thorpe, Bjorn Borg or Lance Armstrong whose comebacks have ended in failure and, in the case of Armstrong, the destruction of their earlier reputation. He could join those in the middle, like Ricky Hatton or Michael Schumacher, who fail to reach the giddy heights of before but still proved something, that they were justified in having a go at returning.

Or, just perhaps, he could return to the top for a final time with all the brilliance of a Paul Scholes, a Michael Jordan, a Sir Steve Redgrave or a Floyd Mayweather.