Argentine left-back Fabian Monzon joined Lyon on a four-year contract on Sunday in a deal that saw French forward Jeremy Pied move in the opposite direction to join Nice.
Lyon annouced the deal on Sunday evening, revealing that they had paid Nice €3m potentially rising to €4m with bonuses.
Pied, 23, joined Nice for €3m, meaning that the only money that will change hands between the clubs will be for any bonus payments that Lyon have to make as part of the terms of the Monzon deal.
Monzon, 25, arrived in France last season and scored eight goals in 34 matches in his debut campaign with Nice.
The seven-cap Argentina international had previously played for Boca Juniors, his formative club, and Spanish side Real Betis, where he spent the 2008-09 season on loan.