The 21-year-old, who still has three years remaining on his current contract, has been strongly linked with a move back to France this summer.
"Chelsea's sporting director Michael Emenalo told me [in July] it will depend on the coach's choices. I explained I would wait to see how it goes in pre-season," he told L'Equipe.
"My decision is definite now. It is an important moment in my career. It is better for me to leave the club and find one where I could play matches regularly.
"Chelsea told me they rely on me. It is nice to rely on me, but I am 21 years old. You can tell me that at 17 years old or 18 years old, but I need to play. I thought more players would have left the club."
Chelsea open their Premier League campaign with a trip to Wigan Athletic on Sunday.