The young striker signed for City on Friday.
"I already knew he was going to Manchester City, as he told me when he came in for international duty on Monday," Riva told Sky Sport Italia.
"He made a lifestyle choice. He'll be playing with a Coach like Roberto Mancini who already knows him well, but it had become impossible to play in Italy, seeing as all it took was his car to run over an ant and he ended up on the front pages.
"He is a talented player and it's in the interests of the Nazionale if he plays more regularly, as he'll be in better condition."