Reyes joined the Gunners in January 2004
|
Atletico Madrid claim Jose Antonio Reyes owes them £1.35m in compensation following his decision to join neighbours Real Madrid on deadline day.
Arsenal rejected Atletico's bid for Reyes last week - but the Spanish side say he signed a contract with them.
Atletico's director Jesus Garcia Pitarch told his club's website: "It included a 2m euros (£1.35m) penalty clause in the event he did not join us.
"Now the legal services of the club will intervene to reclaim this money."
Reyes, 23, moved to the Bernabeu in a season-long loan swap for Brazilian forward Julio Baptista that includes an option to make the switch permanent at a later date.
"In the end, the player did not come and I think it is for the best," Pitarch added.
"All the players here have a degree of commitment and that is the most important thing."