Marcelo has impressed in Brazil's two Confederations Cup games to date and Carlos has said that the 25-year-old improves every game he plays.
"There's no doubt about it, he's the best defender in the world," Carlos told Marca.
"He gets better by the day, a spectacular player. To me he looks happy, and that reflects on how he plays."
Marcelo has 22 caps for Brazil since making his debut in 2006.