Football fans are probably tired of hearing the words 'release clause' in the past few weeks.

Well, it's because they're pretty important in football these days, just ask Atletico Madrid and Barcelona.

On Friday morning, Barca paid Antoine Griezmann's €120m release clause and officially announced his signing from Atletico.

Had such a clause not been in place, Barca may have struggled to have signed the Frenchman, especially after he signed a contract extension last summer.

Given the way he was brought to the club, it will come as no surprise that the Blaugrana have inserted a massive release clause into Griezmann's newest contract.

Unless someone comes in with an €800m bid anytime soon, the 28-year-old will be seeing out his contract at the Camp Nou.

And that mammoth figure is actually bigger than the release clause in Lionel Messi's current contract with Barca.

The Argentine's stands at €700m, so if you've got a spare €1bn, you can sign arguably the world's greatest player for a cheaper fee.

Amazingly, Griezmann's release clause isn't even the biggest in world football.

Karim Benzema is the current holder of that accolade with a €1bn clause, while Brahim Diaz's bizarrely is €750m - also higher than Messi's.

The third highest clause at Barca is Gerard Pique's at €500m.

It's the two Spanish giants that solely dominate the top 10, with Real Madrid having seven players featuring.

Luka Modric (€750m), Isco (€700m), Marco Asensio (€700m), Vinicius Junior (€700m) and Gareth Bale (€500m) join Benzema and Diaz.

The two biggest clubs in world football clearly don't want anyone signing their players, they just want to sign everyone else's...