Isco has signed his contract extension with Real Madrid for four seasons with an option for a fifth.
The deal also includes a €700 million ($827 million) release clause.
"There are no players in Madrid's first-team squad with a clause below 500 million," AS's source explained. "And in Castilla [Real's 'B' team], there are now players with clauses of 300 million."
Isco was linked to a transfer to Tottenham Hotspur last summer and then Barcelona earlier this year.
The injury to Gareth Bale solidified Isco's place with Real Madrid and led to their decision to send James Rodriguez to Bayern Munich.