Aaron Mooy’s transfer to Chinese club Shanghai SIPG may have come as a surprise to some Brighton & Hove Albion supporters.
The Australia international midfielder headed to the Far East in a £4million move – thanks to a pre-existing clause in his contract that would allow him to join a Chinese club for a set fee.
It dates back to Mooy’s time with previous side Huddersfield Town and, after he signed for Brighton at the beginning of last season, he wanted the same clause in his new contract.
That, in turn, has led to his move to Shanghai, which will raise his earnings to £3m net per year.
But what other strange contract clauses in football have there been over the years?
Here, we take a look at some of them.
Stefan Schwarz (Sunderland)
Schwarz had expressed a desire to visit outer space and, at the time, it was believed that commercial space travel would be a possibility in 2002.
And, so worried were Sunderland’s board, that they insisted upon a “no space travel” stipulation in the Swedish international midfielder’s contract.
Indeed, Reid told Schwarz that any potential flights into space would not be tolerated.
Having made only 62 league appearances in his four years with Sunderland, perhaps his prospective space-travelling career would have taken off better than his time in the north east did.
Dennis Bergkamp (Arsenal)
Just the mere thought of having to board an aeroplane made Bergkamp feel ill at ease.
It stemmed, apparently, from his time at Inter Milan, who used small planes for all their away games – which Bergkamp hated.
That proved to be it for the Dutch maestro, who had a clause inserted into his Arsenal contract that he would not have to travel with the club when flying was the only option.
It meant that Bergkamp – who signed for the Gunners from Inter in 1995 – missed numerous Champions League games away from home, although he did make his best efforts to travel by train and car when it was possible.
And it did not deter from him becoming a legend at Arsenal, either.
Giuseppe Reina (Arminia Bielefeld)
Forget a big-headed footballer taking the mickey – this time it was his club which had the last laugh.
When German striker Reina signed for Bielefeld from Wattenscheid in 1996, he insisted on a stipulation in his contract which would see the club build a new house for him for every year he spent with them.
However, because the size of the houses were not specified, the player ended up with a model house made out of Lego for each of the three seasons he spent there.
Reina later signed for Borussia Dortmund – where he won the Bundesliga in 2002.
Dortmund must not have known what to make of it when they found out about his Lego deal with Bielefeld.
Mario Balotelli (Liverpool)
One of football’s most enigmatic characters, nobody – not even notorious taskmasters Jose Mourinho and Roberto Mancini – could put an end to Balotelli’s odd behaviour.
From allowing his friends to set off fireworks in his bathroom, firing air pistols in a Milan square and driving into a women’s prison in Italy because he fancied a look around, the striker’s off-the-field activities can make for incredulous reading.
So when Liverpool bought the former Manchester City man back to England from AC Milan in 2014, they inserted a £1m behaviour bonus in his contract for good on-field conduct.
Balotelli actually only received seven bookings in all competitions for the Reds and was not sent off, either.
But the Italian fell short of expectations at Anfield and soon headed back to Milan on-loan.
Stig Inge Bjornebye (Liverpool)
Sticking with the red half of Merseyside, Norwegian left-back Bjornebye was something of an exotic signing when he joined Liverpool in 1992, as there were few foreign players in the Premier League.
As a child, he had shown an interest in emulating his father, Jo Inge Bjornebye, by becoming a professional ski jumper.
That could have proven a slippery slope for Liverpool, but they imposed a clause which meant that Bjornebye was not allowed within 200 yards of a ski slope.
He went on to make more than 100 appearances for Liverpool during his eight years at Anfield.
Frank Pagelsdorf (Hamburg)
It is rare when a manager and his chairman enjoy a harmonious relationship – but that was exactly the case between Hamburg manager Pagelsdorf and his boss, Uwe Seeler.
In fact, he had a clause included in his contract that enabled him to leave if Seeler, regarded as one of the greatest players in German football history, should no longer occupy the top job.
But, just a few months into Pagelsdorf’s spell at Hamburg, Seeler resigned amid a financial scandal.
However, the clause cannot have counted for much, as Pagelsdorf decided to stay for another three years.
Rolf-Christel Guie-Mien (Eintracht Frankfurt)
Congolese midfielder Guie-Mien made a meal of his contract when he joined Eintracht Frankfurt from Karlsruhe.
For he insisted that the Bundesliga club organise and pay for his wife to attend cookery classes.
She must have learned to cook a mean Frankfurter – which, of course, has its roots in the German city – as well as a host of other tasty dishes.
Neil Ruddock (Crystal Palace)
Former Liverpool defender Ruddock’s health problems have been well-documented, with the Londoner ditching greasy fry-ups for healthier dining options.
He has also cut back on the boozing and cigarettes after having a pacemaker fitted.
But even 20 years ago, there were concerns over Ruddock’s waistline, so much so that West Ham United manager Harry Redknapp – who sold him to Palace – told Eagles’ owner Simon Jordan to put a weight clause in his contract.
That meant that Jordan put a 10% penalty on the deal he was proposing to Ruddock if he was over the recommended weight.
Not that it made much difference to Razor, as his Palace debut was allegedly delayed because the club could not find a pair of shorts big enough for him.
Spencer Prior (Cardiff City)
Sam Hammam’s escapades as owner of Wimbledon are legendary, but perhaps the most bizarre was forcing some members of the Crazy Gang to eat sheep’s testicles.
He carried on that tradition when, as owner of Cardiff City, he signed Spencer Prior from Manchester City in 2001.
Hammam inserted a special clause into the defender’s contract, which stated that Prior would have to have physical relations with a sheep and eat sheep’s testicles before every match.
Perhaps even more strangely, centre-back Prior agreed to the second part of the clause, and duly tucked into the testicles, which are a speciality in Hammam’s native Lebanon.
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Thomas Vermaelen (Barcelona)
It is not unusual for a footballer to have a strop when they are told to play out of their position.
But that was never going to be a problem for Belgium international defender Vermaelen.
On joining Barcelona from Arsenal for £15m in the summer of 2014, he agreed to a clause in his contract which meant that he was obliged to play in whatever position the coaching team deemed appropriate.
Another clause in his deal saw Vermaelen “make the maximum efforts to integrate into Catalan society and learn the Catalan language”.
Vermaelen, who now plays for Japanese side Vissel Kobe, made just 34 league appearances for Barcelona over five years – and stuck to his contract by playing in a variety of positions on the pitch.