A rogue element in European football. Standing alone among 236 clubs, that is how Manchester City are likely to be characterised by Uefa if they fail to agree to a record £50m fine and restrictions on their Champions League squad next season that will severely hamper the ability of Manuel Pellegrini's side to make progress in that competition.

It is not exactly the image Sheikh Mansour bin Zayed al Nahyan was hoping for when he bought the club five years ago and promised to make it a footballing powerhouse. And it leaves the title-chasing Manchester club facing a crucial week both on and off the pitch.

Sheikh Mansour and his colleagues in Abu Dhabi have been determined to paint their unprecedented £1bn investment as something benign that would not only bring the good times back but improve the health of the surrounding area. But that judgment will strike fear – and no little loathing for Uefa – into their hearts.

The proposed sanction – a fine of €60m levied over three seasons and reinvested by Uefa in European football, plus a reduction in the Champions League squad from 25 to 21 players and a salary cap to prevent the overall wage bill increasing further – is a smart mix of sporting and financial measures.

The fine is eye-watering enough to provide a genuine deterrent even to owners of enormous means, while the squad limitations will bite just enough to head off criticism from those who claim it is pointless fining the world's richest clubs any amount of cash. They have the knock-on bonus of allowing Uefa to say it may also help the development of homegrown players, given that eight must be included in the reduced squad of 21.

As a tense stand-off continues between City's accountants, advised by consultants brought in to specifically help with the implementation of FFP, and the investigatory chamber of Uefa's club financial control body (CFCB), the stakes could not be higher.

Given the confidence with which City's executives have reassured the club's owners that they would comply with FFP, there is also bound to be some soul-searching internally.

City have long argued that despite combined losses of a shade over £150m during the two seasons under consideration (2011-12 and 2012-13) they deserve to pass Uefa's financial test. That is because while the rules allow clubs to lose only a total of €45m over two years, they can (for 2011-12) write down the cost of contracts signed before June 2010, investment in facilities and youth development. Uefa also promised to give credit for clubs that show willing, reducing their losses year on year and promising to break even in future.

But City are believed to have been marked down for overinflating the value of their sponsorship deal with the Etihad airline, worth £35m a year, and for creative accounting that allowed them to raise £47m from the sale of image rights and intellectual property in 2012-13.

The Qatari-owned Paris St-Germain, who are under even more scrutiny given the Uefa president Michel Platini's links to the club's owners, have effectively admitted that their jaw-dropping €200m-per-season deal with the Qatar Tourism Authority was overvalued and agreed to Uefa's proposed sanction.

That has left City, convinced that they have engaged positively with Uefa's accountants in contrast to the "haughty" approach of PSG, with a bitter taste at being bracketed with their nouveau riche rivals.

Yet by refusing to accept the punishment on offer in this plea-bargaining routine – an element of FFP added at a relatively late stage as if to underline the involvement of the clubs in the process –City risk isolating themselves.

Platini, realising that he needed the backing of the clubs if his pet project were to work, engaged with the European Club Association at an early stage. In 2010 the ECA agreed to go ahead but negotiated a series of major concessions. That has allowed Platini to argue that FFP was not being imposed on the clubs but also left him open to charges that the elite had co-opted it for their own ends.

If Uefa can make its swingeing penalties stick, it will remove at a stroke the charge that it does not have teeth.

From the 236 clubs under scrutiny, nine ruled to have transgressed have been in negotiation over their proposed "settlements" since last week. Eight have all but agreed to the sanctions imposed, with only City holding out.

It is worth remembering this was an idea originally sold by Platini on the back of a conversation with one of the first wave of overseas mega-rich owners who have changed the face of European football over the past decade. When he first mooted the new "break-even" rules, which in theory would stop clubs spending more than they earned, Platini let slip that he had spoken to Chelsea's owner, Roman Abramovich, about them.

"It's mainly the owners that asked us to do something: Roman Abramovich, [Milan's] Silvio Berlusconi, [Internazionale's] Massimo Moratti," Platini said. "They do not want to fork out any more."

That was inevitably interpreted by many as an attempt by the Russian to pull up the very drawbridge he had rampaged over. Chelsea made a £49.4m loss last year but registered a £1.4m profit in 2012, partly thanks to an £18.4m profit on share dividends and cancellations, so will comply with the new regulations.

Others feared the rules were being so effusively backed by the likes of Manchester United, Bayern Munich and Real Madrid because they saw in them an opportunity to lock in the existing order.

Manchester United, despite being heavily in debt thanks to their leveraged model, had nothing to fear from Uefa's calculations given their huge matchday and commercial income. Arsenal, likewise, had nothing to fear.

Those clubs with huge revenues inevitably fare better under the break-even rules thanks to their natural advantages and the prospect of new, cash-rich entrants being able to make a splash within a short period of time is vastly reduced.

Uefa's general secretary, Gianni Infantino, tasked with implementing Platini's vision, has argued that the introduction of FFP has helped staunch the flow of red ink across Europe and says the "drawbridge" theory does not hold up.

"I would say this is not correct," he told the Guardian last year. "Probably, the contrary will happen. FFP is not about blocking the system as it is. It is healthy and much more sustainable than someone coming in, promising a lot and then the next day the club is bankrupt. Secondly, big clubs have always existed; this will not change.In the past this was attendances, then commercial rights and TV rights."

The argument within Uefa is that FFP was always going to need time to bed in but that this initial tranche of sanctions shows it is serious about making it stick. The worst possible outcome would have been a new set of rules that were blithely ignored by those wielding the largest chequebooks.

Over time, as the level of losses allowed is reduced (it will go down to €45m over three seasons, then €30mover three) so the effect will become more pronounced. And having tackled the precipitous losses of clubs being bankrolled by mega-rich owners, and the distortion of competition it argues that creates, it will then set about trying to improve the competitive balance of European competition. Whether there is anything "fair" about financial fair play will continue to be a matter for debate.

As ever in football, the FFP rules have tended to be viewed through partisan eyes. Manchester City fans see them as a gross distortion of natural competition. Many Arsenal fans see them as reward for careful financial husbandry. But most agree attempting something was better than doing nothing. The question for City's owners is whether they are prepared to trade the goodwill they have built up over five years to fight a Uefa verdict that they see as unfair, first by taking the matter to the CFCB's adjudicatory chamber and then, beyond that, potentially to the court of arbitration for sport. Whether they fold or fight on, the ramifications will be profound.