The 28-year-old striker made his debut with the Rossoneri as a substitute on Thursday.
Cassano set up the match-winning goal that was scored by Rodney Strasser in the 1-0 triumph at Cagliari.
The result extended the Rossoneri's advantage at the top of Serie A to five points over Lazio after the Romans were held by Genoa to a goalless draw in midweek.
"This victory means a lot," said AC Milan coach Massimiliano Allegri. "We have taken three important points especially after our defeat against Roma before the Christmas break.
"It's never easy to win on the road but we did that.
"The team showed a lot of maturity and sacrifice and I'm very happy."
AC Milan will have the team's top scorer Zlatan Ibrahimovic back from suspension and the Swedish forward will lead the attack alongside Brazil pair Alexandre Pato and Robinho.
Allegri has to make a change in goal, however, with Christian Abbiati having picked up a muscular injury.
Marco Amelia will replace Abbiati in goal against Udinese and will have to be at his very best to stop Serie A's leading scorer Antonio Di Natale.
Di Natale increased his tally to 11 goals by scoring his team's second in Udinese's midweek 2-0 triumph over Chievo.
Despite being down to 10 men from the 37th minute after Giampiero Pinzi was sent off, Udinese held on for their sixth home win of the campaign without major scares.
The result lifted them to eighth, level on 26 points with Inter Milan.
"We started the year in the best possible way," said Udinese coach Francesco Guidolin. "Now we face a big test at AC Milan and I'm confident my players will be eager to show their worth on Sunday."
Udinese will have to show a vast improvement as they have lost their last four games on the road.
The hosts will be without captain Massimo Ambrosini, who serves a one-match ban. Midfielder Gennaro Gattuso is doubtful through injury.