Sarr returned to Chelsea on the final day of the winter transfer window, renewing a partnership with Rosenior that proved highly successful earlier this season.

Rosenior, who was appointed Chelsea head coach last month, knows Sarr well from their time together in France, where the defender was a key component of Strasbourg's back line during the first half of the campaign.

"Everyone knows what I think about Mamadou, I think he's got the potential to be a world-class centre-back," said Rosenior, according to the official Chelsea website.

"I'm delighted he's here and thank the sporting directors and ownership for supporting what I thought was the right decision for us and for him in his career.

"I see a growth in Mamadou, even his performance in the AFCON final. I see a growth in his physicality, I see a growth in his tactical understanding. Also, it was an area of the pitch I felt we could strengthen.

"He will get his opportunity, but he knows he needs to fight for it because we have got many outstanding centre-backs in our group."

Sarr's influence extended beyond his performances, captaining the Ligue 1 side on several occasions while on loan.

The 22-year-old arrives on a high after helping Senegal win the African Cup of Nations last month, further enhancing his growing reputation at international level.

Rosenior is excited to work with Sarr again and believes his defensive versatility will be crucial at Chelsea.

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