The reign of Mauricio Pochettino at Tottenham Hotspur is already the 16th longest in Premier League history. Of those above him in the list, only a handful were consistently challenging near the top of the table for the whole of that time. Whatever happens from here, Pochettino’s legacy as one of the most significant figures in English football this decade is secure.

The problem is that nobody quite knows what’s going to happen next. Life in the rarefied air of the Premier League elite can be a precarious existence: it often takes years to build a project, and weeks for it to fall apart. Tottenham have only lost three games. But the way they lost those three games, and the performances in the games they won, will seriously concern a fanbase where a deep-rooted fatalism is never that far from the surface.

Defeat at Inter Milan completed a trilogy of 2-1 losses in which Spurs have shown many of the hallmarks of teams on the slide. Losing leads. Conceding late goals. Brittleness at set pieces. A lack of poise in the final third. They’ve lost to an inferior side, a superior side, and a side roughly on their level. And the scary part is that it could get worse before it gets better.

An alarming but curiously appropriate parallel to make is the Borussia Dortmund side of 2014-15, in what turned out to be Jurgen Klopp’s last season. Like Pochettino’s Tottenham, Dortmund had enjoyed unprecedented success against richer rivals, punching above their weight through an extraordinary team spirit, smart tactics, outstanding levels of collective fitness, and a doctrine of total commitment. If players wanted to leave, Klopp wanted them gone. There was a sort of messianic charm to them, too: a relentless positivity and a beguiling manner that charmed audiences both foreign and domestic.

And then, in the space of a few weeks, it all came apart. A couple of imperfect early wins created the impression that everything was fine on the surface. But the World Cup had squeezed Klopp’s preparation time, and a clearly undercooked squad were exposed in the most brutal fashion. Injuries - the cumulative stress on young players playing high-tensile, full-throttle football for several seasons in a row - began to pile up. Teams had begun to adjust to their style, pressing the central defenders who until recently had been the springboard for so many of their attacks. The defeats kept coming.

By the start of November, Dortmund were in the Bundesliga relegation zone. By the end of it, they were bottom. There were no extrinsic signs of panic, bar the odd tetchy press conference during which Klopp would snap at journalists who had suddenly started turning on him. But the magic had gone. Though Dortmund eventually staged a smart recovery in the spring, finishing seventh in the table despite losing more games than they had won, Klopp was emotionally spent. Before the season was out, he announced he was calling time on his seven years at the club.

Tottenham's players have looked a shadow of their former selves (AP)

So what can Pochettino learn from Klopp’s plight? Primarily, the fact that when the same methods that have brought you success for years on end stop working, they can stop working extremely quickly. The same unshakeable faith and ideological purity that had fuelled the good times can also fuel the bad. Klopp’s inability to countenance a Plan B, and his unwavering faith in the players who had earned him his success, became counter-productive.

Tottenham’s passing game is going to pieces. They showed during last season’s Champions League that they have it in them to play a smarter, more conservative style: the 1-1 draw against Real Madrid and the win against Dortmund at Wembley displayed a more mature, less possession-fixated Spurs. With the midfield well below par and the defence clearly struggling for composure, letting the other team have the ball for a bit might not be the worse idea. The blueprint is there; whether they want to adopt it is another matter.

It’s not a perfect comparison, of course. The Bundesliga, for all Bayern’s dominance, is a good deal more equal than the Premier League. Smaller clubs regularly challenge at the upper reaches of the table; big clubs can easily end up in a relegation fight. Tottenham are in no immediate danger of slipping into genuine trouble. But already it looks like the top four, not the top spot, will be their upper limit this season.

Mauricio Pochettino must adapt to the situation he is now facing (Getty)

Nor are Tottenham haemorrhaging players to their biggest rival like Dortmund were, in the shape of Mario Gotze and Robert Lewandowski. But equally, the lack of signings this summer has generated a certain staleness. “You need change to make the next step in the team’s development,” Klopp once said. “If I say ‘go left’, they would say, ‘you’ve told us that 200 times, we don’t want to hear your voice any more’.” Five seasons is a long time for the same players to be hearing the same voice, on the same training ground, dispensing the same messages. Does Pochettino have it in himself to adapt?

Mostly, though, Tottenham’s main enemy is financial gravity. Spurs are still some way behind the Premier League’s top five in terms of revenue generation, even before you factor in the impact of their new stadium. In the long term, Tottenham are well-placed to gatecrash the elite. But in the short term, the lesson of modern European football is that even the best sides can only punch above their weight for so long.

“We still believe in each other,” Erik Lamela insisted. “I don’t think we’re losing our confidence. Of course, people are thinking like this. But inside the dressing room, I can tell you it’s not like this. We believe in this team. It’s time to win again.”