Atletico Madrid are under increasing pressure to sell Radamel Falcao this summer.
El Confidencial says Porto have gone public to announce they are owed by Atletico €28 million for the sales of Falcao and Ruben Micael.
Atletico chiefs have already admitted they may be forced to sell due to the debt owed to Porto.
Falcao is a top target for Chelsea owner Roman Abramovich and a sale would quickly calm Atletico's money men.
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