Gusto, who has played in France's under-21 team, has played 15 times in Ligue 1 this campaign after the 19-year-old broke into the starting lineup last season.

Financial details were not revealed but Sky Sports said the transfer fee was 26.3 million pounds ($32.60 million).

"The defender will now continue his impressive progress on loan at the Groupama Stadium before joining up with the Blues in the summer ahead of the new campaign," Chelsea said in a statement.

Gusto is Chelsea's seventh recruit in the mid-season transfer window after the London club signed Mykhalo Mudryk, Benoit Badiashile, Noni Madueke, Andrey Santos and David Fofana while Joao Felix arrived on loan from Atletico Madrid.

Chelsea are 10th in the Premier League, 10 points from a top-four spot. They next play Fulham in a London derby on Friday.