Sampdoria sporting director Carlo Osti has welcomed the teenager on-loan.
"Petagna is an attacker who we will need," Osti told Tele Nord. "Milan sold him to us because he wouldn't have had much space there and we are delighted to have netted him.
"He's a young guy, who is very good with his head, but it is important that we don't place too much responsibility on his shoulders."
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