The Rossoneri are keen to secure a replacement for Brazilian Thiago Silva, who recently secured a big-money switch to Paris Saint-Germain.
Papadopoulos had been tipped to join Manchester United on the back of an impressive Euro 2012 campaign with Greece.
However, the 20-year-old's agent Paul Koutsoliakos doubts a move would be possible this summer.
"AC Milan interested in my client? There is much speculation about the guy these days," he told calciomercato.com.
"Papadopoulos has another three years on his contract with Schalke, a club where he is very good, so a transfer to Italy would be very difficult.
"Whoever wants him would first have to speak with Schalke."
Papadopoulos has established himself as a key member of the Bundesliga side following his move from Olympiakos in 2010.
