All soccer fans must feel they know something of Chelsea owner Roman Abramovich after his 15 years in the game, but, truth be told, it is hard to discern much about him. Despite being one of the highest-profile figures in British public life, he is a deeply private man.

What is plain to see is that he is a survivor, having emerged from the tumult of the former Soviet Union to become one of the 100 richest people on earth. Yet despite a talent for strategic thinking, he appears a man of impulse. He had not watched a single game of live football between elite clubs until he attended Manchester United's thrilling 4-3 win over Real Madrid at Old Trafford in 2003, or so the story goes.

That Cupid's arrow of a match ignited a love affair with the sport. Shortly afterward, Abramovich was browsing London football clubs for a multimillion-pound investment, as we might sift through shirts on a retail rack. Eventually he plumped for the blue one: Chelsea. This was little more than a discretionary purchase for the Russian billionaire, but it changed the course of football.

Chelsea had been in financial meltdown, but he proceeded to pour tens of millions into an unprecedented trolley dash of transfer trading. It made such a splash that the waves are still being felt today. English football owes much to the impact of that wild summer and the sustained spending it spawned in West London. It would break the Arsenal-Manchester United duopoly and propel the Premier League onto a global stage.

These 15 seasons of Chelsea's new paradigm have brought great success: five Premier League titles, five FA Cups, Champions League and Europa League trophies. Throughout, Abramovich has looked down from on high in his private box at Stamford Bridge, smiling broadly and offering polite applause.

That is the story of the recent past, which has certainly been kind to Chelsea fans. But the present and future bring uncertainty.

On the pitch, Chelsea went from winning the Premier League last season to falling out of the top four. But it's off the pitch, with rumours surrounding Abramovich's Chelsea future, that things are really intriguing.

Abramovich's application to the UK Home Office to renew his visa was declined. Those close to him claim he withdrew it. Whatever the truth, it seems to have prompted him to apply successfully for Israeli citizenship.

At about the same time the visa issue was unfolding, Abramovich put on hold plans to build a new stadium for Chelsea. Staff at Chelsea talk privately about their confidence that Abramovich remains committed to the club, but what if he stops funding it?

The first thing to point out is that, for all their success on the pitch and the revenue that generates, Chelsea have benefited from large amounts of shareholder subsidy in recent years.

Abramovich has been pouring, on average, around £60 million a year into Chelsea. Technically, it has not been largesse but loans, and the most recent count, made in June last year, said the club owed its owner some £1.2 billion. This is repayable within 18 months of Abramovich calling it in -- a commitment Chelsea would naturally be unable to meet if he did -- although at that time he did not express any intention of demanding repayment.

In the five years between the 2011-12 and 2015-16 seasons, the most recent period for which all clubs' accounting records are available, Chelsea were English football's third-highest wage-payers, behind Manchester City and Manchester United. In 2013-14, they were comfortably the highest net spenders on transfers, investing £96.4m more than they recouped. Yet in terms of revenues, Chelsea have generally been only the fourth-richest club in the Premier League.

The Chelsea board has sought to rein in rampant spending. In 2016-17, with no Champions League revenue, the wage bill unusually fell by 1.2 percent to £220.9m. But to compete at the top of English and European football, a club can only cut back so much. This is why Abramovich had been seeking to expand Stamford Bridge and bring in the kind of corporate and ticketing revenues that allow the likes of Arsenal and Manchester United to be self-sustaining. This might not happen now, so what next?

One positive consequence of not building a new stadium is that it would cut out a good deal of development costs. Between 2014-15 and 2016-17, Chelsea's net capital expenditure -- that is, money spent on land, building and renovation projects -- has added up to £119.4m. Though high in recent years, this has traditionally not been the biggest element of Chelsea's investment, which has instead been the money spent on players.

The problem for Chelsea is that, if Abramovich turns off the tap, they would need to become self-sustaining, and that could be hard to maintain. If they were to rely on the cash they generate themselves, Chelsea would be forced to operate at a different end of the transfer market.

Despite winning plaudits for canniness in the market, Chelsea spend tens of millions of pounds more on transfers than they generate in free cash flow. And more buying will be required in the years to come: The 11 players that manager Antonio Conte used most frequently this past season have an average age close to 27. Refreshment will be needed before too long.

And keeping the lid on wages will become difficult. Eden Hazard, Willian and Cesar Azpilicueta are entering the final two years of their deals, a point at which their transfer value diminishes and pay raises are usually sought. Meanwhile, Thibaut Courtois, David Luiz, Gary Cahill, Cesc Fabregas, Pedro and Olivier Giroud have only 12 months remaining. Chelsea will hope the prospect of a new Premier League TV deal will cover the inevitable wage inflation that renewals bring, but it cannot be guaranteed.

In only two of the past six seasons have Chelsea had substantially more than £10m in cash left over after core expenditures on wages, travel, utility bills, insurance and the like. It is unthinkable that Conte, who has repeatedly complained during the season about what he perceives as a lack of financing for new players, or a new manager would be satisfied with a net transfer budget of less than £10m annually.

The picture may soon get worse before it gets better. Having failed to finish in the top four, Chelsea will be second-class citizens in Europe when they play in the far-less-lucrative Europa League next season. With that revenue stream falling and stadium income effectively remaining flat, this would be a hard time for the club to have to live within their means.

And so the focus remains on Abramovich and whether he will continue his policy of subsidy. If he were to walk away, other suitors might perhaps take on one of world soccer's biggest brands. But, like so much else around Chelsea's inscrutable owner, no one can know that for sure.