[3] Tassi made his Serie A debut at the age of 16 years and 99 days, making him the ninth-youngest player ever to debut in Serie A; he came on as a substitute for Brescia in a 2–2 draw at home against Fiorentina on 22 May 2011, and played the last 15 minutes of the match.
[4][5] Already dubbed the "new Roberto Baggio" by the club's president at the time, Luigi Corioni, due to his playing role, style, and promising performances for Brescia at youth level,[2][6] on the last day of the transfer market in the summer of 2011, Internazionale signed him on a co-ownership deal with Brescia for €2 million,[7][8] meaning he would play for Inter's youth team during the 2011–12 season.
Due to his young age, he played in Allievi Nazionali U-17 team in his first year with the club.
[16] A talented midfielder, Tassi is a quick player with a good feet and slender build, who is good on the ball, and dangerous in attacking areas due to his ability provide assists for teammates or score decisive goals.
Widely regarded as one of the most exciting prospects in Italian football of his generation in his youth, his characteristics and playing role drew comparisons with Roberto Baggio, and also Andrea Pirlo.