Sarr's adaptation to life in England has been helped by three key factors. First, he spent a month with the team during their pre-season in the United States, where Chelsea won the Club World Cup, allowing him to bond with his new team-mates.

Second, the appointment of Rosenior - whose footballing philosophy Sarr knows well - has encouraged a player once defined by physicality and height to add greater intensity and aggression to his game, both on and off the ball.

Those close to the young defender say he explored loan moves to Premier League and Champions League clubs in the summer following the Club World Cup, only for Rosenior to persuade him to return to France as Strasbourg vice‑captain while competing in the Uefa Conference League. They add that, had Rosenior not replaced Enzo Maresca in January, Sarr had expected to remain at Stade de la Meinau until the summer.

Third, Senegal's Afcon triumph gave him the greatest moment of his career so far, having started the final as a replacement for the suspended Koulibaly.

Since agreeing his move to Chelsea, Sarr has taken two hour‑long English lessons every day and has...