How were Chelsea able to spend so much in January and what does it mean for the future of Leeds United's Premier League rivals?

We live in an era of financial fair play, where limits are put on what clubs can spend to stop them having an unfair advantage over their rivals, and to create them storing up future problems if a benefactor dies, loses interest in the club or, as in the case of Roman Abramovich, is forced to leave.

Despite that, Deloitte calculates the Stamford Bridge club spent more on gross transfer expenditure than the combined total of all clubs in the Bundesliga, La Liga, Serie A and Ligue 1, the four richest league's after England.

They spent £430m signing Enzo Fernandez, Mykhaylo Mudryk, Benoit Badiashile, Noni Madueke, Malo Gusto, Andrey Santos and David Dietro Fofana. Thye also loaned striker Joao Felix from Atletico Madrid at great expense.

Spending on that scale is impossible for clubs such as Leeds United – who beat them 3-0 in August – to compete with.

They were able to because of a legal accounting method called amortisation, which allows them to spread the cost of signings in the books over the length of a contract.

It is why Fernandez and Mudryk signed an eight-and-a-half year contract, and Badiashile, Madueke seven-and-a-half. Gusto and Fofana signed for a mere six-and-a-half-years.

Such contract lengths are highly unusual in football. Santos' five-and-a-half years is more like the top end for elite players.

It means that for accounting purposes Fernandez's British record transfer fee of £107m goes down as just £12.6m per year, even though it will almost certainly not be paid to Benfica this way.

If at any point they sell him, the fee received will be booked as a lump sum.

FIFA are now looking to introduce a rule which means fees cannot be amortised over more than a five-year period.

It does not come without risk, however. To an extent Chelsea are mortgaging their future for short-term gain.

If Fernandez sees out his contract, it will take £12.6m out of the Blues' budget each year, plus his expensive wages. Chelsea will no doubt be happy to pay them if the Argentinian consistently reproduces the performances which saw him voted the young player of the World Cup.

But if Fernandez does not fill his potential or meet the requirements of any of Chelsea's managers between now and 2031, finding someone else to take on those wages could be difficult.

If it were just him, that would be one thing, but the risk also applies to Mudryk, Badiashile, Madueke, Gusto, Santos and Fofana. It would be a surprise if all were successful signings.