Arthur has gone AWOL from Barca after a move to Juventus was confirmed.
Malcom told Marca: "He is my friend and one of those I speak to the most.
"In a few years he will be one of the best players in the world for his quality. He is a footballer committed to the club, a worker who always wants to be at a good level."
Of his own problems at Barca, Malcom added: "Since I was little it was my dream to play for Barça. I played and enjoyed every day with the best in the world. I will be able to tell my children and grandchildren that I played for this team."