It can be strange for those of us who remember Manchester City in the pre-money years to think that their new generation of followers might never fully understand why Joe Royle used to talk about a debilitating condition, unique to the club, called “Cityitis”. Suffice to say, though, that it could be particularly virulent at times and Royle, in keeping with many managers, never did go through with his promise to find the antidote.

“Poor old Joe,” Colin Shindler reflected in his book Manchester City Ruined My Life. “He never understood that Cityitis is not a bacterial infection that can be cured by the antibiotics of running a club in a professional manner. Cityitis is a vitamin deficiency we are born with. We can take supplements to build our immune system but they are not strong enough to deal with diseases like Thakin Shinawatra or signing Jamie Pollock from Bolton Wanderers.”

It also goes back further than you might realise bearing in mind the story of City winning their first league championship in 1937 and following it up the next season, spectacularly, by finishing the highest scorers in the league. Wilf Wild’s team beat Derby County 6-1 at home, 7-1 away, scored another six against Leeds and West Bromwich Albion, knocked five past the title-chasing Charlton Athletic and finished with three more goals than Arsenal, the champions.

The problem was City also managed to lose 20 times that season and were relegated. They would have stayed up with a draw in their final game, or if any of their fellow strugglers – Grimsby, Portsmouth, Birmingham and Stoke – were beaten. All four won, City lost and found out in the dressing room they had become the only top-division team in history to go down with a positive goal difference.

Then a second bulletin came through that Manchester United had won promotion, on goal average, and would be taking their place. File it as the first recorded outbreak of Cityitis, not least because one of their shots that day came back off the stanchion inside the goal and the referee, 40 yards away, thought it hit the crossbar.

Seventy-nine years on, that is still the only occasion in this country when a team have been relegated after winning the league the previous year, though not perhaps for much longer judging by the latest evidence that Leicester City have taken over as the most eccentric team in English football.

How, after all, do you make sense of a team who stayed up after six months in the relegation zone two seasons ago, won the league by 10 points the following year and now find themselves back in the quicksands?

Who could have possibly imagined, even in the absurd world of football, that Claudio Ranieri could be named as Fifa’s world coach of the year, with all that talk of another statue being commissioned to go with the ones in Leicester’s city centre honouring Gandhi, Richard III and Thomas Cook, and that within a few weeks he would be the bookmakers’ favourite as the next manager to be sent to the guillotine?

And has there ever been a clearer example of what can happen in sport when the people who have encountered success fall into the trap of believing their own publicity and forget what made them so formidable in the first place?

Unfortunately for Leicester, this is always the risk for any group of players who have enjoyed the view from the top and must know, deep down, they will never experience the same kind of professional joys again. Players lose their edge, sometimes in the most subtle and insidious ways. Complacency, the football manager’s enemy, spreads. After that, it is virtually impossible to generate the same hunger. The rot sets in.

Riyad Mahrez, such an elegant destroyer of defences last season, has scored three league goals, all penalties.

Something similar happened at Manchester United, albeit to a lesser degree, when they won the European Cup in 1999. “For months afterwards, the treble haunted us wherever we went,”Roy Keane once said. “Well into the following season, we were being saluted as heroes, history-makers, better than the 1968 team, the team of the century – signing photographs with the three trophies, talking about that ‘great night’ that we’ll never forget.”

Sir Alex Ferguson’s team won the Premier League the following season but in Europe, their Achilles heel, they did not reach another final for nine years and maybe their captain was on to something when he linked it back to that sweet-scented night at Camp Nou. A couple of players, Keane recalled, said in post-match interviews it did not matter if they never won another trophy again. “‘Hello’, I thought. Overexcited, maybe, but what the fuck are we going to do next year? Is that it? We’ve made history. Now we pack it in? It doesn’t matter what we do now, we’ll never be forgotten.”

Dwight Yorke scored 29 times in 52 appearances for United in the 1998-99 season, led the line superbly and set up countless chances for others. Beyond that point, however, he seemed more devoted to being a playboy and the sport is littered with other examples of players who have been softened by success. Just look at Blackburn Rovers after their title triumph. Or the deterioration in Samir Nasri after winning the league for the first time at Manchester City. And, yes, the players of unfashionable, unheralded Leicester City.

Jamie Vardy and Riyad Mahrez are the most dramatic examples when they have followed their clean sweep of last season’s player-of-the-year awards by sleepwalking through what loosely passes as a title defence. Has the rot set in with them, too? Leicester were once such a grounded, unpretentious bunch it would have been unimaginable to think they could allow their competitive instincts to be dulled.

Not any longer, though. And a small thing, perhaps, but does their owner, Vichai Srivaddhanaprabha, understand now why some seasoned observers felt slightly uneasy about the entire squad, including substitutes and bit-part players, turning up at the start of the season to find a treat – a fleet of BMW 18s, costing £105,000 each – waiting for them outside the ground to recognise their new status as league champions?

This is not to ignore the ramifications of N’Golo Kanté’s departure that led to Ranieri pretending to throttle his former player when they crossed paths before Chelsea’s win at Leicester a few weeks ago. Kanté made 14 tackles in Chelsea’s midweek assignment at Liverpool, compared with Leicester’s total of eight against Burnley. He is not the type of player to dribble past three opponents, fire shots into the top corner or pass the ball with the outside of his boot. He has, however, put in more successful challenges than anybody in the Premier League over the past three seasons. Which is some feat when he has been here only 18 months.

All the same, it still feels like a cop‑out to attribute all of Leicester’s issues to the loss of one player. For all his talents, Kanté was never expected to head the ball away at corners. It was not his job to put in crosses for Vardy, or weigh in with 10 goals a season. He might have given the impression sometimes he was football’s equivalent of the Duracell bunny but don’t hold him responsible for the way Robert Huth, Wes Morgan, Danny Drinkwater, Kasper Schmeichel, Vardy, Mahrez and all the others have allowed their fires to dim.

For Ranieri, it must be dispiriting that stories are now emerging of dressing-room divisions, that opponents are hearing Leicester is a place of egos and bad attitudes, and stories are being leaked that undermine a manager who, in happier times, called his players his “babies”, rang a pretend bell and happily admitted that, yes, he was a bit teary.

These kind of leaks generally do not happen when a manager has full control and the players are united. Leonard Ulloa’s public mutiny offers its own insight into the fractures behind the scenes and, in Mahrez’s case, would it be unfair to point out that there are times in football when signing a contract does not necessarily equate to complete devotion?

Mahrez’s new deal was announced in mid-August but only after it became apparent he did not have any counter‑offers from a bigger club. What went unreported at the time was that his pay rise was accompanied by the kind of verbal agreement that is commonplace in these situations, meaning that if he played well enough to attract an offer from one of Europe’s superpowers his current club would not hold him back at the end of the season.

Perhaps it just isn’t so easy to replicate a high level of form when you are operating with those kind of blurred priorities. Mahrez, such an elegant destroyer of defences last season, has scored three league goals, all penalties, and perhaps it is not a coincidence that he has reserved his best performances for the Champions League, in keeping with the team as a whole.

All of which represents some turnaround when it was this weekend a year ago that Ranieri’s men went to Manchester City for one of their season-defining fixtures, won 3-1 and delivered a free-wheeling performance that left nobody in any doubt we were witnessing a beautiful, baffling story. “Ninety minutes in Manchester changed everything,” David Bevan, author of The Unbelievables, later wrote. Yet here we are, a year on, and a largely unchanged team are suffering their own version of Cityitis. It is a wild graph and it is not going to be easy to get the needle pointing upwards again.

On a knife edge in Toulon

David White’s autobiography was, in his own words, a “life-changing, soul‑searching journey” when it involved the former Manchester City, Leeds and Sheffield United player having to go through the harrowing events that led to him coming out last November among the former footballers who have been victims of sexual abuse.

Yet there are other layers to Shades of Blue and one story in particular is worth recounting from the Toulon tournament in 1988 when England’s under-21 players were allowed a night out and White headed to a bar with Michael Thomas, Nigel Clough, David Platt and Paul Gascoigne.

Everything was fine, White reports, until one of the locals took offence to something Gascoigne had said, pulled out a flick-knife and held it to the throat of the man who was about to become the most expensive footballer in Britain. And it was there, operating to a strict 10pm curfew, that a small group of England’s bright young stars must have wondered how they were going to explain this one to their manager Dave Sexton.

Gazza managed to escape without injury and the knifeman-in-France story does not make the cut in his own autobiography. “Which perhaps gives an indiction about how eventful his life would become,” White concludes.