The 26-year-old has sealed his long-awaited move to the Serie A outfit for 3.3 million euros, signing a four-year deal
The Argentina international had been linked to the club for much of the summer but prolonged negotiations were thought to have scuppered the deal.
However, the Rossazzurri confirmed they had reached a compromise with les Gones over a sale, with the upfront fee believed to be in the region of 3.3 million euros, while a further 300,000 euros could be paid on performance-related bonuses.
The 26-year-old had struggled to adapt to life at the Stade de Gerland following a €3m move from Nice last summer and spent the second half of last season on loan with Fluminense in Brazil.
Monzon has earned six caps for la Albiceleste.