AC Milan and loans Petagna started his football career in
AC Milan's
youth system, where he was a member of the under-15 squad who won the
Campionato Nazionale Giovanissimi in 2010 and a member of the under-17 squad who won the
Campionato Nazionale Allievi the following year. He made his professional debut on 4 December 2012, coming on as a
substitute in the late stages of a
UEFA Champions League group stage home game against
Zenit St. Petersburg, which Milan lost 0–1. At the start of the 2013–14 season, Petagna was promoted full-time to the first team. He made his
Serie A debut on 24 August 2013, coming on as a late substitute in the opening game, a 2–1 away loss against newly promoted
Hellas Verona. However, following the acquisition of
Alessandro Matri in the late days of the summer transfer window, Milan decided they would let Petagna go out on loan to
Sampdoria in order to gain more first team experience. Sampdoria also had the option to make the deal a
co-ownership agreement at the end of the season-long loan spell. In spite of that, the loan was terminated early and Petagna returned to Milan in January, having made five scoreless appearances during his stay at Sampdoria. He finished the season with three more senior appearances, while being mainly employed by the
under-19 squad managed by
Filippo Inzaghi. The side won the
Viareggio Cup in February, defeating
Anderlecht in the final, with Petagna scoring the equaliser for the
rossoneri in a 3–1 win. On 16 July 2014, Petagna was loaned out to
Serie B side
Latina ahead of the 2014–15 season. On 13 January 2015, he was signed by
Vicenza on loan. On 30 August 2015, he was signed by Serie B newcomers
Ascoli on loan.
Atalanta and Ascoli loan On 25 January 2016, Petagna signed for
Atalanta and was loaned to former club Ascoli until 30 June 2016.
SPAL On 19 July 2018, Petagna signed for
SPAL on loan until 30 June 2019 with an obligation to buy. He scored his first goal with
S.P.A.L. in his debut match on 12 August, scoring the final 1–0 goal in the
Coppa Italia third round match against Spezia He scored his first
Serie A goals with the Emilian side on 17 September, scoring a double that allowed the Biancazzurri to beat his former side Atalanta 2–0.
Napoli On 30 January 2020, Petagna signed with
Napoli. He stayed at SPAL on loan until the end of 2019–20 season.
Monza On 12 August 2022, Petagna joined newly promoted Serie A side
Monza, with an obligation for purchase if certain conditions are met. He made his debut for Monza on 14 August, as a starter in a 2–1 Serie A defeat to
Torino. On 19 October Petagna scored his first goal for the
biancorossi, sealing the 3–2 comeback win in the round of 32 match against
Udinese. On 31 October, he scored the first goal Serie A goal for Monza, from a
penalty kick, momentarily giving his side the advantage in the home match against
Bologna, which eventually ended in a 2–1 defeat. When Monza guaranteed
survival in the Serie A, Petagna's obligation-to-buy clause was triggered, forcing the
Lombardy club to permanently acquire the striker for a reported total cost of €14 million.
Cagliari (loan) On 30 August 2023,
recently promoted to Serie A side
Cagliari announced the signing of Petagna on a season-long loan from Monza, with an option to make the move permanent. ==International career==