Thomas Tuchel started this transfer window with the clear intention of reinforcing his defensive options following the departures of Antonio Rudiger and Andreas Christensen.
Not only were those senior players of a quality capable of competing in the Premier League and Champions League, they also had suited Tuchel's defensive style at Stamford Bridge, with Rudiger reaching performance levels he had never attained previously in a Chelsea shirt.
The signing of Kalidou Koulibaly felt like the perfect response to losing a presence like Rudiger, with the Senegal international coming to England as one of Europe's strongest defenders over the past decade.
