The Genoa-based club have confirmed the signing of the talented attacker on a temporary basis with the teenager joining until the end of the current season
The 18-year-old, who came through the club's youth system, made his professional debut for the Rossoneri in a Champions League group match against Zenit St Petersburg on December 4, 2012, which his side lost 1-0.
He was made a full-time member of the senior squad at the beginning of this campaign and played his first Serie A match on August 24 against Hellas Verona, in which Massimilano Allegri's men were handed a 2-1 defeat.
Petagna could make his first appearance for his new club in the derby against Genoa, which will be taking place on September 15.
Sampdoria will have the option buy acquire 50 per cent of the rights for the Italy Under-19 international in the future.