Europa League winners Atletico Madrid still owe FC Porto €28.6 million for the transfers of Falcao and Ruben Micael, according to a report in AS.
The Spanish side signed the duo from the Dragons in a combined deal of €45 million last summer.
Falcao scored two goals in this season's Europa League final as Atletico won their second European title in three years. Meanwhile, Micael joined Real Zaragoza on loan for the 2011-12 campaign.
In a report sent to market accounts and made public, it highlights that Los Colchoneros have yet to pay off the transfer fee, with €28.6 million still owed to the Portuguese giants.
The transfer fee was sanctioned in August 2011 under the mediation of agent Jorge Mendes, with Atletico confident that they will meet the payments agreed between the two parties.
Atletico ended the Primera Division season in fifth place.