Paris - Cristiano Ronaldo, Lionel Messi and the rest of the world's top footballers may earn eye-popping salaries but the sums they make from long-running boot deals can be equally astounding.
In July 2017 the new face of French football, Kylian Mbappe, pursued by Europe's elite clubs, caused a frenzy of excitement by announcing on Twitter he had a big announcement to make.
Would he choose Real Madrid? Paris Saint-Germain?
But what the 19-year-old actually had to announce was that he was extending a deal he first signed with Nike at the age of 13.
And within weeks he had moved on loan from Monaco to PSG, who are also sponsored by Nike.
It's not just a case of lacing up the customised boots and picking up the fat cheques though - the high earners are brand ambassadors and have stringent public relations commitments.
"It's not like having a job and being an employee working for an employer," explains image rights specialist Frank Hocquemiller.
"But with a sponsorship deal there come certain obligations. If you have signed a deal with Adidas, Nike or Puma, it means they have bought your image rights.
"It comes with a certain amount of public relations requirements and social network management."
The aim of sportswear companies is clear - raising visibility for their product, and they believe paying millions is worth it.
"The sportswear companies are investing more and more money and they want a return," explains Kevin Geoffroy from Footpack.fr, a sportswear news site.
So Twitter, Instagram or Snapchat accounts of the stars are harnessed by the sportswear giants to push their product.
Arsenal and Germany midfielder Mesut Ozil recently advertised Adidas on his Instagram account, where he pointed out he had a paid relationship with the German brand. That pay is reportedly in the region of £3.7 million a year.
Most top players have similar deals. France and Manchester United midfielder Paul Pogba recently signing a muti-year deal with Adidas worth a reported €40 million.
David Beckham retired in 2013, but continues to plug Adidas products and his celebrity lifestyle plays perfectly into the current sportswear trends. So out with the football boots, in with the black Adidas tracksuits for the arrival lounge at Los Angeles' LAX airport.
No prizes for guessing that Real Madrid's Ronaldo enjoys the most lucrative soccer boot deal in history, with his contract with Nike thought to be worth £6.2 million a year.
To give an idea of the bidding war that pushes up the value of these contracts, the current Nice and former Manchester City and Liverpool striker Mario Balotelli put pen to paper with Puma ahead of the 2014 World Cup for a rumoured £5.1 million per year. The Italian's career has had so many stops and starts since, it is doubtful he still earns anywhere near that sum.
Using footballers to promote products is nothing new. In the 1930s Andre Abegglen, the Swiss centre-forward at French club Sochaux, launched his own footwear brand with the slogan: "For a good worker, good tools, to a good footballer, good boots."
There have always been clashes of interest too.
Dutch great Johan Cruyff would only play for his national side if they took off one of the three Adidas stripes from his shirt as he had signed with French brand Le Coq Sportif.
He would later sign with Puma, and picked up one of his Ballon d'Or awards with the brand's logo emblazoned on the pocket of his dinner jacket.
In France's 1998 World Cup win, coach Aime Jacquet narrowly avoided a players' strike from disgruntled players baulking at wearing Adidas boots for the national team because of their own private deals. The players won that World Cup wearing Adidas, but ever since they have been able to wear what they want.
Another anecdote from the France set-up suggests however that for the 2014 official World Cup team photo, regardless of height, only players wearing Nike boots were allowed to sit in the front row - because Les Bleus' shirts are made by the US giant.