The small print of a football players contract is one of the sport's greatest enigmas, with plenty of bizarre clauses popping up all over the place.
Typically they are done to prevent clubs losing players on the cheap or keeping their notoriously bad behaviour in check.
But there have been some truly bewildering agreements put in place at top Premier League clubs and across Europe's top leagues.
Some clauses are put in purely to spite other clubs, some are done to protect either the player or the club, or some appear to be just for a giggle really.
So here's from Firmino's anti-Arsenal proviso to Bergkamp's flying demands, here's the 10 of the strangest transfer clauses out there.
Roberto Firmino
Liverpool and Arsenal don’t really get on when it comes to transfer business after the Gunners once submitted a bid of £40million + £1 bid for Luis Suarez to get around small print in his deal.
The Reds got their own back by including a €98million release clause in Firmino’s contract “if the interested club is not Arsenal ”.
Giuseppe Reina
German striker Reina demanded his club Arminia Bielefeld build him a house for every year of his contract.
They outsmarted him though and built it out of LEGO for all three years of his deal. Brilliant.
Dennis Bergkamp
There’s a reason world-class forward Bergkamp didn’t play in many European away matches. He had a no-fly clause in his contract.
Philippe Coutinho
Some more astute business from Liverpool, they included a clause in Coutinho's £142m move to Barcelona that means the Blaugrana must pay £89m if they try to pinch any more of their players before 2020.
Mario Balotelli
One of the Premier League’s bad boys with plenty of wasted talent, Balotelli had a ‘good conduct’ clause when he joined Liverpool to ensure he wouldn’t step out of line.
Maybe the lack of antics were the reason he underwhelmed at Anfield.
Luis Suarez
This is a unique clause for a truly unique man - but when Suarez joined Barcelona from Liverpool they added in a ‘no biting’ clause given the striker’s history.
Ex-Nou Camp president Josep Maria Bartomeu has denied any talk of such a clause, but they’ve both left now so who knows if it was true or not?
Matija Nastasic
Schalke players were only permitted to wear Adidas boots when former Manchester City defender Nastasic signed in 2015.
But the Serbian provided a medical note to prove he could only wear his Nike numbers instead.
Samuel Eto’o
It’s no secret that footballers get a taste for the high life.
That is quite literal in the case of Cameroonian striker, who demanded Russian club Anzhi Makhachkala give him a private jet so he could live in Moscow and fly to training every day.
Ronaldinho
You may think a night club clause could prevent players from going out.
However, in this case of party animal Ronaldinho, he had a clause that meant he could go out clubbing more than usual (at least twice a week) without any repercussions.
Stefan Schwarz
Last but by no means least, when Schwarz signed for Sunderland from Valencia in 1999 it appears he had other career aspirations too.
The Sweden international had plans to go into space at some stage, so the Black Cats had an agreement that meant they could cancel his contract if he left the planet. Strange.
