Monachello was called up for the squad in
Allievi Nazionali U-17 team and also participated in The
2011 Granatkin Memorial in Moscow which took place from 3 to 9 January 2011 In March 2012, he signed a contract with
SC Tavriya, which was confirmed in June 2012. But two weeks later, in July 2012 it was announced that his club would be
FC Metalurh Donetsk of the
Ukrainian Premier League. In January 2013, Monachello left Metalurh Donetsk for
Olympiakos Nicosia on a free transfer signing for six months. Monachello then transferred to
AS Monaco in June 2013. Two months later it was announced that he would play on loan for Monaco's Belgian partner football club
Cercle Brugge until the end of the 2013–14 football season. He made his debut on 10 August 2013, coming on as a substitute in the 57th minutes, as Cercle Brugge and
Lierse drew 1–1. His first goal came on 5 October 2013, when he scored the club's first goal game before setting up the second in a 2–1 win over
Mechelen. He mostly came on as a substitute in the second half, as his minutes significantly decreased. After five months at the club, his loan spell with Cercle Brugge ended.After the end of the loan Gaetano had to choose his next station for his career. Despite interest from Bolton, Bournemouth and Blackpool he chose his next team to be the Cretan side Ergotelis F.C as he played for the 2013-14 season scoring two goals. Monachello signed for
Atalanta on 23 July 2015. Monachello signed for
US Palermo on 31 August 2017. On 15 January 2020, his loan to
Pordenone was terminated early. On the same day, he was loaned to
Venezia. On 3 October 2020, he moved to
Serie C club
Modena on a permanent basis. On 25 January 2022, he was transferred to
Serie C club
Mantova on a permanent basis. On 26 July 2024, Monachello joined
Lumezzane on a two-season deal. ==International career==