Kaka played for Milan between 2003 and 2009 before joining Madrid, where he has failed to make a huge impact in three years.
The 30-year-old has been strongly linked with a move back to the Rossoneri, and midfielder Ambrosini says that he will be welcomed by everyone at the club.
"Kaka is welcome here at Milan," Ambrosini is quoted as saying by La Gazzetta dello Sport.
"Everyone would like it if he came back. Kaka is one of those players who left Milan despite still having some unfinished business.
"He is a great player who still has a lot to give. In my opinion, it does not seem like he has any physical problems."
Kaka is currently with Madrid on their pre-season tour of the USA.