The France centre-back looks set to make the switch to Massimiliano Allegri's side after being suspended by his current club for criticising team-mates and manager Miroslav Djukic for Valencia's slow start to the the campaign.
Los Che president Amadeo Salvo confirmed on Wednesday that Rami has opened negotiations with the Rossoneri and Niang - who faced the 27-year-old when the two sides clashed in pre-season - is confident he would prove a sound acquisition.
"Rami is a great defender," the striker told Sky Sport Italia.
"I knew him in the United States and also saw him in the France side, so I can say he's a very good player.
"We hope his qualities can help the team."
Milan have slumped to 12th position in Serie A, having taken just eight points from seven matches so far this season and the 18-year-old is desperate to help the club achieve a spot in the Champions League through their league position.
He added: "I hope that this season I will score more goals. I have to work hard, but the important thing is that the team wins.
"Our objective is to finish in the top three, as we are a great team with quality players. I believe we can do it."