Tottenham Hotspur bosses have reportedly angered Real Madrid by demanding that they be paid up front for the sale of Luka Modric.
The two clubs are believed to have agreed a fee in the region of £35m for the 26-year-old's transfer.
However, the Spanish champions are now threatening to call the deal off because Spurs refuse to be paid in instalments, according to The Sun.
Real begin the defence of their La Liga title with a home match against Valencia on August 18.