"The agents and the player signed a pre-contract agreement which included a two million euro penalty clause if the player did not play for Atletico this season," sports director Jesus Garcia Pitarch told a news conference on Friday.

"Our legal services will intervene to claim this money on behalf of the club."

Spanish international Reyes has denied signing a pre-contract agreement with Atletico, saying it would have been illegal.

After Real's initial approach appeared to be rebuffed last month, Atletico stepped in and made an offer for Reyes.

Arsenal eventually rejected Atletico's bid and completed a loan swap with Real late on Thursday night in which Brazilian forward Julio Baptista moved to London in exchange for Reyes.