The Belgian goalkeeper was full of praise for the Catalan side, and Lionel Messi in particular, in the wake of last weekend's 5-0 loss
The Vicente Calderon club were hopeful of achieving a positive result against the Catalans, but they were trailing 2-0 within 15 minutes and were eventually heavily beaten.
"Barcelona play football from another planet. I feared for a real thrashing after their good opening, and, to be honest, it was a bit of a whipping in the end," Courtois was quoted as saying by Sporza.
"We started the match too timidly and paid them too much respect. We should have shown a bit more flair."
Courtois then went on to praise Lionel Messi, who netted a hat-trick on Saturday, as he feels the Argentine is the best player in the world.
"It's quite a special feeling to see him dribble in real life. He definitely is the best player in the world."
Atletico have dropped to eighth spot in the Primera Division following their loss, while Barcelona now sit second in the table.