Jose Mourinho is a fan of young French defenders. Having played a major part in kickstarting Raphael Varane's career at Real Madrid, he's since brought in Kurt Zouma at Chelsea, and according to Duncan Castles at One World Sports he's hoping to land another this summer. This time he's after Lyon's Samuel Umtiti, a 21-year-old who can play either at left back or centre half.
Umtiti would certainly seem to fit the profile for Chelsea's signings -- he's young, good, and significantly experienced despite his age, helping Lyon to a second-place finish behind Paris Saint-Germain with 35 league starts last season. If Mourinho thinks he can play left back to a reasonable level, he can provide cover for Cesar Azpilicueta should Filipe Luis actually want to leave, but the general thinking around him seems to be that he's a centre back long term.
Since there are only two years left on his deal, he shouldn't be too expensive either. Castles reports that Lyon are looking for around €15 million for him. That certainly seems reasonable enough, but let's wait and see how this all turns out.