Leandro Paredes has joined Zenit from Roma in a deal potentially worth up to EUR27million.
The 23-year-old midfielder, capped once by Argentina, has agreed a four-year contract with the Russian Premier League side.
Roma confirmed they have agreed a minimum fee for the sale of EUR23m, which could rise by up to EUR4m based on team and player performance bonuses.
A product of the Boca Juniors academy, Paredes initially joined Chievo on a temporary basis in January 2014 and was then loaned to Roma in July of that year.
He signed permanently for the Giallorossi from Boca Juniors in June 2015.
Paredes, who has scored four goals in 37 Serie A appearances for Roma, spent the 2015-16 campaign on loan at Empoli.
He received his first Argentina cap from new head coach Jorge Sampaoli in the 6-0 friendly win over Singapore in June.
Paredes follows expensive Liverpool acquisition Mohamed Salah in leaving Roma, who have brought in Rick Karsdorp and Lorenzo Pellegrini.