The 21-year-old was on loan last season at Ajax Amsterdam, who finished runners-up in the Dutch top flight, scoring nine goals in 24 league games.
Ajax also reached the Europa League final where they lost to Manchester United having knocked Lyon out in the semi-finals when Traore scored twice.
He joined Chelsea from Burkina Faso's Association Jeunes Espoirs De Bobo-Dioulasso in 2013 and went on loan to Vitesse Arnhem the following year.
Traore returned to make his Chelsea debut just after his 20th birthday in a Champions League game against Maccabi Tel Aviv in September 2015.
He netted four goals in 16 appearances for the west London club including scoring in three consecutive games in 2016.
Lyon finished fourth in Ligue 1 last season to qualify for the Europa League.
(Writing by Ken Ferris; Editing by Alison Williams)
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