Pato cannot play a competitive game for Milan until the transfer window reopens in January, but the 18 year-old Brazilian will be fielded in tonight's friendly against Dynamo Kiev.
Ancelotti said: "He will be on the field tomorrow and we hope he can settle in to the squad well, although obviously we'll give him plenty of time for that. We are happy he is here.
"He can play many friendlies with us, especially in the breaks for international duty. We expect to see something of his remarkable quality right from tomorrow. He is a real striker and very fast."