Theo Hernandez upset many at Atletico when he chose to leave last summer for city rivals Real.
The move so far hasn't worked out for the fullback, but his older brother believes he can still prove himself good enough at Real.
Lucas told France Football: "It's his decision. He wanted to take another path. But that proves that he believes in himself. It's his first season at Real.
"He fits in well. He is only 20 years old."