Bakayoko then moved to AC Milan on loan and spent last term at Monaco, the club where he made his name, playing 23 times in all competitions and scoring once.
Born in Paris, Bakayoko came through the Rennes academy in the north-west of France and made his senior debut in August 2013, a week after his 19th birthday.
He signed for Monaco the following summer and featured in almost 100 games for the principality side during his three seasons there before joining the Blues, scoring five goals.
In 2016/17 he starred as they unexpectedly beat Paris St-Germain to the title and also reached the last four of the Champions League, knocking out Manchester City and Borussia Dortmund en route. Bakayoko scored the decisive goal in a thrilling two-legged tie against the Premier League side.