Chelsea inserted a clause in the deal that means Atletico would have to pay them extra money for every time Courtois appears against them.
Some reports claim it is as much as £4million per match, although the exact figure has not been confirmed.
However, Atletico president Cerezo has confirmed that the clause does exist and if the two teams are drawn together, then Courtois is unlikely to feature.
Speaking to Spanish radio Onda Cero, he said: "It is a figure that we cannot pay."