The forgotten 25-year-old is unhappy at how his January transfer to Le Havre collapsed.
While he is still at Chelsea and earning his wages, Sarr is training with the Under-21s and is not in the club's long-term plans.
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According to The Athletic, Sarr has never been so down as he has been in recent weeks.
They said: "I have never seen him as low as this. This is the first time I have seen him like this. He tries to change his mental state.
"But it is hard when you are not playing. He is not in the first-team dressing room anymore, he is with the kids in the other building.
"He feels outside the group. He tries to hide his feelings, but I know him, what he is really feeling."