Robinho started his career with Santos and was linked with a move back to the Brazilian club in the January transfer window, but nothing materialised as reports suggested that a fee could not be agreed.
The 29-year-old was loaned back to Santos from Manchester City in 2010, but then moved to AC despite being keen on making the loan into a permanent move.
That may be a possibility now, with Santos vice-president Odilio Rodrigues confident that a deal will be done.
"Santos don't know what value AC have set, but we should get the answer to that question soon - probably this week," said Rodrigues.
"We will work based on what Milan and the player demand. We will then transmit this information to the club's board, and depending on the value they will decide if signing him is feasible. I believe it is."