Born in the province of Bergamo, he grew up in the youth teams of Bolgare and then Atalanta, who loaned him to Palazzolo and Montichiari, before returning to Bergamo. He made his Serie A debut for the club on 14 March 2010 in a league match against Parma, coming on as a 79th-minute substitute for Simone Tiribocchi. Following his debut, Gabbiadini made one further appearance for the club during the 2009–10 Serie A campaign.
On 9 July 2010, Gabbiadini joined Serie B side Cittadella, along with Daniele Gasparetto, in co-ownership deal for a peppercorn of €500, as part of the negotiation that saw Atalanta sign Matteo Ardemagni. He scored five goals in 27 appearances, including 15 starts, during the 2010–11 Serie B season.
On 17 November 2010, Gabbiadini made his debut with the Italian under-21 squad in a friendly game against Turkey. On 29 March 2011, he scored his first goal for the U21 team in a friendly game against Germany. On 6 October 2011, he scored a hat trick in the away match won 7–2 against Liechtenstein. He took part at the 2013 UEFA European Under-21 Championships in Israel, scoring two goals against hosts Israel in the group stage, as Italy went on to reach the final, only to lose to Spain.