The two clubs have been trying to settle on a deal for the 29-year-old but are yet to come to an agreement.
"Robinho wants to go back to Santos," Galliani told Sky Sport Italia. "We will see if we will find an agreement.
"In the last few hours, there has been a further approach, but there isn't an agreement yet.
"We will start looking for another striker only when Robinho leaves. We have a good team and five strong forwards."
Robinho joined the Rossoneri from Manchester City in 2010 after a spell on loan at Santos.