Dmitry Rybolovlev made $6.5billion when in 2010 he sold his shares in Uralkali, the potassium mining company he built up since the mid-1990s. He is an astute investor who has looked for a return in other sectors too. In 2008 he spent $95million on the Maison de l’Amitie, an 18-bedroom Palm Beach mansion he bought from Donald Trump, a huge commitment but one that he is still confident of making a profit on.

And yet now Rybolovlev is trying to make a profit on the hardest investment portfolio of his life: footballers.

The story of Monaco’s recent development and their radical change in direction is well-known now. They famously spent €165million on players in the summer of 2013, signing Radamel Falcao, James Rodriguez and Joao Moutinho, three top-end Jorge Mendes clients who could have played for any team in the country.

But the most important signing they made that year, given everything how things have turned out, was Anthony Martial. He joined for €2million from Olympique Lyonnais, where he was a teenager still finding his way from the academy into the first team. He soon found his way into Monaco first team, coached by Leonardo Jardim. In 2015 Manchester United, wanting to add some pace and edge to their front line, paid €50m up front for Martial, with another €30m in likely add-ons.

Earlier that summer Monaco had tied Martial to a new deal and he had been declared, along with Bernardo Silva, ‘intransferable’ by the club. But when the money Rybolovlev had no hesitation. “[He accepted] with no qualms,” French journalist Arnaud Ramsay writes in his new biography of Rybolovlev, “because from his point of view, economic logic will always win out over sporting logic.”

Falcao and Moutinho both arrived in the 2013 transfer window (AFP/Getty)

That makes the transfer of Martial one of the most profitable ever recorded in football. At first glance it might look like freak good fortune. Except for the fact that Monaco are likely to make an even bigger profit this summer from Martial’s successor at the Stade Louis II, Kylian Mbappe.

Monaco signed Mbappe for free when he was 15, even after he had been shown round by Chelsea at 11 and Real Madrid at 14. But Monaco are brilliant at identifying young talent and Mbappe has been a phenomenon in Jardim’s first team, setting the record as their youngest ever player then as their youngest ever goalscorer. When Mbappe shredded Manchester City with his pace at the Etihad Stadium last month, it was with the eyes of Europe’s biggest clubs all on him.

The biggest auction in Europe this summer will be for Mbappe, with Real Madrid, Barcelona and Wednesday’s opponents City all making him a top priority. Monaco are open to selling him but they will demand even more money than they got for Martial. He will likely go for €60m, aged 18 and a half.

Martial only spent two seasons at the Stade Louis II (Getty)

Monaco, clearly, are as good as it gets when it comes to buying low and selling high. It is not just explosive forwards they pick up as teenagers either. They signed Aymen Abdennour for €15m and sold him to Valencia for twice as much. They signed Geoffrey Kondogbia for €20m and sold him to Internazionale for twice as much. They turned a healthy profit on James Rodriguez even if his performances for Real Madrid have not yet justified the €80m they spent on him after his brilliant 2014 World Cup for Colombia.

Even if Mbappe goes this summer, there are still players who could fetch huge prices this year or beyond. Tiemoue Bakayoko is an imposing holding midfielder admired by many in England. Djibril Sidibe and Benjamin Mendy are the most dangerous pair of young full-backs in Europe, who destroyed Tottenham in the group stage and will cause City serious problems tonight. And Bernardo Silva, the jewel in their crown, is a brilliant little number 10 who could play for any team he wanted.

Mbappe is the club's newest star (Getty)

It is a tribute to the long-standing scouting and academy team who work at the club, as well as the direction of Rybolovlev and his vice-president Vadim Vasilyev. Plenty have left but they keep replacing them with quality. Lucas Campos, the Jorge Mendes associate who found many of these players, now works for Lille, but the club signed a good replacement in Antonio Cordon, formerly of Villarreal.

For all the criticism made in 2014 that their project was going to go the same was as Anzhi Makhachkala, they have in fact become stronger on the pitch this season even as they continue to sell players just as they come good. That is why they are top of Ligue 1, three points clear of Paris Saint Germain, a club who continue to throw money at problems in a way that Monaco have grown out of.