Kylian Mbappe is set to become 60m euros (£52.5m) richer after winning a battle for unpaid salary and bonuses against his former club Paris St-Germain.

One aspect of Mbappe's legal victory raised eyebrows - PSG were told they must hand over 1.5m euros (£1.3m) in "ethics bonus" payments to the France forward.

For football fans in the UK, an ethics bonus might sound a little strange, but in France, it is a normal part of a professional athlete's contract.

The "ethics bonus" has made headlines before, primarily when details of Neymar's PSG contract were revealed by Spanish newspaper El Mundo.

The Brazil forward's deal stipulated a monthly ethics payment of 541,680 euros (£475,876). For Mbappe, the bonus was worth 500,000 euros (£438,000) a month.

Reports picked up on clauses that required Neymar to show "courtesy, friendliness and availability to supporters". He was also expected to "greet fans before and after each game".

The truth behind the ethics bonus is very different.

What is an 'ethics bonus'?

In English football, clubs are able to fine a player up to two weeks' wages for a misdemeanour.

French law forbids any deductions from a worker's salary. Sports teams, therefore, make a small portion of it an ethics bonus. The base wage and the ethics bonus are in effect a player's total salary.

In 2021, it was claimed in some reports that Neymar received extra money for clapping the fans, but the details paint a different picture.

Neymar was expected to behave responsibly to sponsors and referees. He had to turn up to training on time and was barred from placing bets. In effect, it was a moral code.

"Clubs are very keen to protect their image," football finance expert Kieran Maguire told BBC Sport.

"They don't want anybody going nuclear and criticising the club, which means that they call them good behaviour clauses.

"We saw similar with Tiger Woods and Lance Armstrong [who had morals clauses with sponsors]. So behavioural clauses are quite common within sport."

In 2018, Marco Verratti had part of his ethics bonus withheld after being caught drink-driving.

Hatem Ben Arfa also lost the bonus when he failed to attend PSG's mid-season training camp in Qatar.

In 2023, Lionel Messi was punished by PSG after making an unauthorised trip to Saudi Arabia.

Rugby union club Racing 92 took action against winger Teddy Thomas by "retaining his ethics bonus for February" after an incident following a Six Nations match between France and Scotland.

Star players can earn 'another 40%' in bonus payments

Bonuses are now a large part of a player's contract. They cover loyalty payments, received each year on the anniversary of a player joining a club, through to image rights and goal bonuses.

"The contract, which used to be written on the back of a napkin, is now an investment by a series of stakeholders," Maguire said.

"You've got the club, you've got the agent, you've got the management company, you've got the player. And quite often, the player's intellectual property rights company as well.

"I've seen some of the big six contracts, and there are 25% uplifts for Champions League participation."

The world's best players are in such high demand they could earn huge top-ups through their image rights, as high as "60% basic and another 40% on top of that", Maguire added.