There's an old saying that "greed is a bottomless pit", but that's not proving to be the case for Paris Saint-Germain.

The Ligue 1 champions-elect are in fact finding that there are some constraints despite the ludicrous levels of financial backing they have received from their Qatari owners.

Last summer, Neymar became the most expensive player in the world when he left Barcelona for the Parc des Princes in a £198million switch.

Within a matter of weeks, Monaco announced their young prodigy Kylian Mbappe would be following in his footsteps.

The agreement was that the French international would initially sign for PSG on loan and the deal would be made permanent at the end of the current season, with the principality club then receiving £167m.

The 19-year-old has contributed a respectable 19 goals in all competitions in his debut season in the capital. Given that Edinson Cavani is not only 31-years-old, but also facing an uncertain future at the club, it was hoped that they could rely on Mbappe as the future.

PSG may be forced to cash in 

However, the Mirror report that amid UEFA's investigation into whether they have broken Financial Fair Play regulations, there is a genuine fear that the Parisians face being kicked out of the Champions League, as well as being fined.

European exile is simply not an option as they seek to become a superpower, so they could be forced to sell some of their more lucrative assets.

It's claimed that Manchester City are therefore optimistic Mbappe could become available, just a year after he turned down a host of elite clubs around the continent to stay in his homeland.

Pep Guardiola even visited him last summer to try and lure him to the Etihad.

Legally, there is no way PSG can get out of giving Monaco their money. So, the option being explored by the newspaper is that they would buy him and then sell him on a short time later.

It could be an anxious summer amid widespread reports that Unai Emery will be replaced with Thomas Tuchel and with the threat of sanctions continuing to loom.

Where should Mbappe go if he has to leave PSG? Have your say in the comments.