Leonardo replaces Rafa Benitez whose contract was terminated by mutual consent just before Christmas.
“I am happy with Leonardo's arrival,” Materazzi told Sky Italia. “It's no disrespect to Milan.
“I am convinced that we will get back to winning ways with him.”
Materazzi also gave his reaction to the signing of Italy international centre-back Andrea Ranocchia.
“For me, Andrea can do very well in the blue and black shirt. I already see him as a new Alessandro Nesta.”