The 28-year-old featured for 45 minutes in his side's 2-1 win over Siena that sealed third spot in the Serie A table last weekend, but went under the knife this week to resolve a knee problem.
"AC Milan wishes to communicate that Giampaolo Pazzini has undergone surgery on his right knee," a statement on the club's official website reads.
"The operation took place in Namur, Belgium and was successfully completed by Prof. Martens. The player is expected to return to action within four to six months."
Pazzini joined Milan from Inter at the start of the 2012-13 campaign and netted 15 goals in 30 league appearances for the Rossoneri.