Manchester United and Real Madrid could face sanctions from UEFA if the governing body decides to focus its Financial Fair Play rules on clubs who owe debt.

The aforementioned sides owe £350 million and €600 million, respectively, as reported by Richard Jolly of ESPN FC. UEFA's scheme currently targets those in European competition who fail to balance the books on a season-by-season basis, even if they owe no debt.

UEFA general secretary Gianni Infantino believes the emphasis could switch, per Jolly: "We're now focused on losses, and to repay the debt is part of the loss that the club can make at the end of the season. But, certainly, the question of debt is something that can be put on the table."

Essentially, this means clubs such as United and Madrid could be penalised for simply owing money, even if they break even across the inspected time-frame.

The opposite situation showed itself when Manchester City were fined and handed a transfer cap during UEFA's first run of punishments.

No debt is sat against the club and the accumulated expenditure is financed by Sheikh Mansour's Abu Dhabi United Group. This is perhaps more sustainable than the model United and Madrid offer, as noted by City chairman Khaldoon al Mubarak when his side received sanctions, as reported by the club's official website and via Jolly:

We have a sustainable project today, in Manchester and across the board in the City Football Group. We have zero debt. We don't pay a penny to service any debt. For me, that is a sustainable model. However, our friends at UEFA seem to believe otherwise. They have their view, we have ours.

It's certainly a debatable point, particularly when you consider the FFP dossier opens by saying it aims to improve "the overall financial health of European club football." Unpaid debt certainly has the potential to be harmful in the long run and is an insidious way of running any team.

Although United have managed to halve their debt in the last decade, per Jolly, the lavishness of their major purchases and contracts are offset by the ominous sense the club is working beyond its financial means while the debt remains. A similar picture unfolds at Madrid.

Questions should certainly be raised as to how Madrid afforded the £86 million fee of Gareth Bale when their debt sat at £500 million. United, too, recently paid a British record transfer sum of £59.7 million for Angel Di Maria.

Both numbers, plus the players' wages, could have seriously impacted the club's fight against debt. But on the other hand, funds accumulated from their arrival (shirt sales, sponsorship deals, etc) may eventually help the clubs to break even. 

UEFA's FFP rules are certainly a work in progress. Both sides, and many others, will be fearing the possibility of debt being taken into account. The European governing body has a duty to ensure all teams remain financially safe, however, meaning this could be a necessary step.