The Italian coach has expressed his views on the club's Champions League first knockout round draw, and believes his old side have a very difficult task ahead of them
But the 66-year-old believes the Rossoneri could cause an upset if Barca are not at their best.
"Watch out for Milan because they have a lot of international experience. If Barca are at their best it will be very difficult for Milan to qualify, but if they are not then Milan can win," he said.
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"Barcelona are on another level now, but Milan cannot be under-estimated."
The former Real Madrid director of football also touched upon the return of Bojan to Camp Nou, with the 22-year-old set to face his old side for the first time since leaving them in 2011.
"Bojan is playing pretty well," Sacchi said. "He doesn't always play but he is improving in Italy."
The Italian coach also expressed his sadness at the news that Blaugrana coach Tito Vilanova has suffered a relapse of a tumour he first suffered with last year.
"When I found out about Vilanova's relapse it hurt me a lot. I am convinced that he will fight it with everything," he said.
Barcelona finished top of Group G on 13 points after their six fixtures, whereas Milan finished second in Group C behind Spanish club Malaga, accumulating eight points from their six games.