The French youngster, 19, has been immediately loaned back to the Ligue 1 club until the end of the season.

Zouma has been one of Chelsea's top targets in the transfer window, and Jose Mourinho sees him as a long-term replacement for the ageing John Terry.

The strong centre-back has represented France at all youth levels, and has put pen-to-paper on a five-and-a-half year contract.