The Premier League side recently signed the Belgian from Genk and, regarding him as one for the future, have sent him straight on loan to the Spanish side.
Courtois, 19, passed a medical on Friday morning in the Spanish capital and completed the necessary paperwork, and will train with his new team-mates for the first time on Sunday.
Atletico were in the market for a goalkeeper after David De Gea's departure to Manchester United this summer.
Source: Team Talk
Source: Team Talk