Unsurprisingly, Real Madrid and Barcelona dominate the list of stars with the biggest buy-out fees included in their contracts
How much would it cost to sign Cristiano Ronaldo or Lionel Messi?
It is a question often debated by football fans but the only definite answer - the price that would force Real Madrid and Barcelona to give up their star men - comes in the form of their release clauses.
Release clauses are most prominently a feature in La Liga, where Spanish law requires that every player is able to buy out their own contract.
This normally happens with the club interested in that player paying them the money with which they can then activate their release clause, making it effectively a transfer fee.