Modric’s stock rose at the 2018 World Cup, where he helped Croatia to the final, where they lost 4-2 to France.
The 32-year-old performances were enough to earn him the World Cup’s Golden Ball for most outstanding performer.
Inter Milan are believed to be interested in signing Modric, but Perez has now made it clear it would take a mammonth offer to lure the midfielder away.
“The only possibility that Modric leaves is by paying €750 million,” Perez told reporters on Thursday.
Modric has a contract that runs through June 2020 with Madrid.