The Belgium international has nothing but praise for the in-form hitman, and believes his colleague was perfectly entitled to declare for Spain over his native Brazil
The 24-year-old striker has filled Radamel Falcao's boots admirably following the latter's summer departure for Monaco, scoring eight goals in only seven games.
Spain coach Vincente Del Bosque has successfully persuaded the Brazil native to declare for la Roja and Courtois believes the forward will excel at international level.
"Diego is a great striker," he told reporters. "He is always difficult to stop in training. We'll see which country he chooses to play for but it is up to him who he wants to play for."
Courtois also hailed the cosmopolitan nature of the Rojiblancos squad, which he believes has contributed to his side's fine start to the season.
"For Atletico it is good that we have so many internationals, but not just for Spain," the keeper continued.
"I and Tony Alderweireld play for Belgium, there is Arda Turan, there are the Uruguayans. This means we are doing things right and we need more work like that.
"We now need to work well with humility and with our feet on the ground."
Diego Simeone's men are on a roll with five consecutive Primera Division victories, the highlight being last week's 1-0 victory over local rivals Real Madrid at the Santiago Bernabeu.