The Belgian international is currently in his third season on loan from Chelsea, but as it stands, is due to return to his parent club at the end of the season.
Simeone is actively pursuing a permanent deal, however, and has claimed that he would be prepared to pay "anything" for the 21-year-old's services.
"For me anything we pay for Courtois is cheap. He's a young guy with a huge future and is on track to be one of the best goalkeepers in the world," Simeone said on Spanish television.
"Signing a goalkeeper of his calibre would be a big step. It won't be easy. It depends on what Courtois wants. We know what the club needs to do but it's not up to us, he's not our player."
Courtois joined Chelsea from Genk in 2011.