Milan's squad captain Massimo Ambrosini gave his backing to Boateng's actions, insisting a "message had to be sent against uncivilized people."
"I am sorry for all those who were at the stadium but a strong message had to be sent," said Ambrosini.
"AC Milan will make an effort to go back to Busto Arsizio especially for the children and for those who have nothing to do with racism but a message had to be sent against such uncivilized people."
AC Milan director Umberto Gandini added on Twitter: "Very proud of the Milan players who decided to walk off the pitch today for racist abuse from few idiots! No racism, no stupidity!"
Milan returns to league action on Sunday against Siena.
Meanwhile, World Club Cup winners Corinthians has announced it has agreed a $19.6 million deal with Milan for Brazil striker Alexandre Pato.
The 23-year-old, who joined Milan in 2007 from Internacional, scored 63 goals for the Italian giant during his five-year stint with the club.
But his career has been hampered by injuries in recent years, with the forward managing just 11 appearances last season and seven so far this campaign.
"In the coming days, Pato, who will wear the number seven shirt, will undergo a medical and then sign a four-year contract," said a club statement.
Milan confirmed the deal on its official website: "AC Milan can announce that Alexandre Pato has been sold outright to Sporting Club Corinthians Paulista."
In an open letter on the club's website, Pato said: "I wish to salute and especially thank everyone. From the president to the many people I worked with in these unforgettable years at Milan.
"I am going to Brazil, to Corinthians, so I'll have the opportunity to play consistently. It will not, however, be easy to forget Milan.
"I will always be tied to this jersey, the club colors and all the Rossoneri fans. Above all at this moment my thoughts and my biggest thanks go to them."