On 20 July 2017, Mosti was loaned to Serie C side Gavorrano on a 6-month loan deal. On 27 August, Mosti made his Serie C debut for Gavorrano, as a starter, in a 2–1 away defeat against Livorno, he was replaced Simone Zaccaria in the 77th minute. On 5 November he scored his first professional goal, as a substitute, in the 91st minute of a 2–2 away draw against Monza. On 30 December he scored his second goal, again as a substitute, in the 88th minute of a 4–3 away defeat against Olbia. In January 2018 his loan was terminated and he return to Juventus leaving Gavorrano with 15 appearances, 2 goals and 1 assist. On 27 January 2018, Mosti was signed by Serie C club Viterbese Castrense on a 6-month loan deal. Two weeks later, on 11 February, he made his Serie C debut for Viterbese as a substitute replacing Claudio De Sousa in the 87th minute of a 2–0 home win over Gavorrano. Five more weeks later, on 17 March, he played his first entire match for Viterbese Castrense, a 2–0 home win over Arezzo. Mosti ended his 6-month loan to Viterbese Castrense with only 9 appearances, including 6 as a starter, and making 1 assist, however he didn't play any entire match during this second part of the season.
On 24 August 2018, Mosti was loaned to Serie C club Imolese on a season-long loan deal. On 18 September he made his Serie C debut for Imolese in a 0–0 home draw against AlbinoLeffe, he was replaced after 54 minutes for Michael De Marchi. On 21 October he scored his first goal for Imolese in the 29th minute of a 3–1 home win over Rimini. On 22 January 2019, Mosti scored his second goal in the 32nd minute of a 2–0 away win over Teramo. On 9 February he scored his third goal in the 18th minute of a 3–2 away win over Gubbio. On 31 March he played his first entire match for the club, a 2–1 home win over Triestina. Mosti ended his season-long loan to Imolese with 39 appearances, inclunding 26 as a starter but he played only one entire match, scoring 6 goals and making 4 assists.
Loan to Monza
On 2 August 2019, Mosti was loaned to Serie C club Monza on a season-long loan deal with option to purchase which could became obligation if Monza reach the promotion in Serie B. On 25 August he made his debut for the club as a substitute replacing Cosimo Chiricò in the 78th minute of a 2–1 away win over Pro Patria. On 8 September he scored his first goal for the club, as a substitute, in the 91st minute of a 1–0 away win over Como. On 22 September he played his first match as a starter for the club and he also scored his second goal in the 49th minute of a 3–0 away win over Lecco. Mosti ended his season-long loan at Monza with 18 appearances, three goals, and one assist, helping the club win the Serie C and gain promotion to the Serie B after 19 years.
Monza
After being promoted to the Serie B, Mosti became a Monza player outright.
