Real Madrid have reportedly set Brahim Diaz's release clause at £674m following his arrival from Manchester City.
The Spanish midfielder returned to his home country earlier this week on a six-and-a-half-year contract after struggling for first-team appearances at the Etihad Stadium.
Madrid may pay up to £21m for Diaz when various add-ons kick in, and the European champions are keen to protect their investment for the long term.
According to Spanish outlet Sport, the get-out clause in the 19-year-old's contract is worth more than triple the current world transfer figure, held by £198m Paris Saint-Germain forward Neymar.
Diaz, who is believed to be on wages of more than £3m a year at the Bernabeu, is in line to make his Madrid debut against Leganes on Wednesday night.
