Flaccadori came through the youth ranks of Excelsior Pallacanestro Bergamo,[1] before transferring to Basket Treviglio, where he made his debut for the club's men's team in the amateur Italian third division during the 2013–14 campaign.

He played 26 games in his first year in men's basketball, averaging 2.5 points a contest.

[2] Flaccadori then joined Dolomiti Energia Trento of the professional Italian top-flight level league Serie A in August 2014.

[3] In his first season with the team, he saw the court in 34 games in the Italian League, scoring 2.8 points per outing.

[6] On 31 July 2019 Flaccadori signed a two-year contract with Bayern Munich of the German Basketball Bundesliga (BBL) and the EuroLeague.