Some of those transfers, of course, are simply traditional loans that have worked out well. Others may have been loans with an “option” to buy for a set fee, should the player prove a success. In many cases, though, they follow the Mbappé model: loans which are, in essence, deferred sales. According to one executive, the language is a little misleading: so as not to arouse the suspicions of UEFA’s auditors, the “obligation” has to be dependent on something, but the bar is often set so low that it is impossible not to meet it.

The appeal, in many cases, echoes P.S.G.’s intentions: a deferred purchase enables clubs access to a better quality of player than it might otherwise be able to acquire immediately while complying with F.F.P. It is why, for example, Barcelona’s most recent offer to P.S.G. to reacquire Neymar was not a purchase, but a loan-to-buy deal structured along the lines of Mbappé’s.

There are benefits to these arrangements for the clubs seeking to offload players too, and not only in reducing salary commitments at a time when wages have become so inflated that few clubs outside of Europe’s richest leagues can afford elite salaries. As far as clubs’ accountants are concerned, a guarantee of future income enables teams to forecast more accurately their total revenues for the seasons ahead. “It’s a relatively new concept, but it can be a sign of good practice,” Chaudhuri said.

It is not the only way F.F.P. has started to mold the transfer market, though. “There are so many types of creativity available to the clubs,” said Esteve Calzada, the chief executive of the agency and marketing firm Prime Time Sport, and a former chief marketing officer at Barcelona.

Long-term loans have grown in popularity — Chelsea has sent three strikers to Atlético Madrid on such terms in recent years — while the recompra, a contract clause that has long been a feature of transfers in Spain, in which the selling club has the right to buy back a player for a set fee, has spread across Europe.