Courtois is on loan at the La Liga club from Chelsea, but was forced to play against his parent club in the Champions League semi-finals.
However, the Belgian shot-stopper was coy on how it had affected his decision on where to play next season, with Blues boss Jose Mourinho able to bring home his player if he so desires.
"My future seemed clear but then we played (against Chelsea) in the Champions League," Courtois told Belgian newspaper La Derniere Heure.
"And yes, Mourinho called me before the (La Liga) game against Barcelona.
"What we talked about stays between us. I have a two-year contract with Chelsea, so in principle I will be there for training, then we'll talk.
"This isn't the time to think about a transfer. There's a World Cup at stake."
Courtois is reportedly afraid of returning to Chelsea, as he might remain behind incumbent Petr Cech in the pecking order.
And whether Courtois will be a number two is the story of his situation, as the young keeper could be edged for the top role of Belgium's team in Brazil by Simon Mignolet.
The 22-year-old said that he would accept the decision of coach Marc Wilmots, though, if he was to be left out.
"I'm ready. I trained Friday and Saturday and I'm in good shape," Courtois said.
"But I haven't played with this defence and it's different with Atletico.
"If he chooses Mignolet, I can't argue."
Courtois also reflected on Atletico's heart-breaking Champions League final loss to Real Madrid, in which the latter reigned 4-1.
Sergio Ramos' injury-time equaliser powered past a hapless Courtois in the Atletico goal, and Real went on to score three more in extra-time to seal their 10th European title.
Despite a valiant effort, Courtois said he still lost sleep over Ramos' game-changing goal.
"I felt empty and I couldn't sleep," he said.
"I woke up several times through the night thinking about Sergio Ramos' header.
"I nearly stopped it. I only missed by a few centimetres.
"But we can't forget that we won the title this season."
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