The 21-year-old Burkina Faso international spent last season on loan at Ajax Amsterdam, his third season in the Eredivisie after a two-year spell at Vitesse.
Lyon president Jean Michel Aulas revealed that part of the €10m deal will see the Blues earn 15% of the profit from a future sale, and will also have first refusal.
Traore scored nine goals in 23 Eredivisie appearances last season, and also scored a brace against his new employers in last season’s Europa League semi-final.
Meanwhile, Aulas is also hoping to secure the services of Real Madrid striker Mariano Diaz, and told L'Equipe that they "are closing in on a transfer".
"If we can come up with the resources to make it happen then Mariano is our priority," Aulas told L'Equipe, via The Daily and Sunday Express.
"He does have other more economically appealing options. However, we know from [Zinedine] Zidane and [Karim] Benzema that he is a player with a lot of quality."