The Champions League winners disclosed that Castillo would spend the 2021/22 in the Championship at Birmingham City.
Chelsea had last season loan, Castillo to ADO Den Haag after ending his loan deal with AZ Alkmaar.
The Premier League giants disclosed this in a statement via their website on Tuesday.
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The statement read in part, “Juan Castillo is embarking on his first loan in English football having previously had loan spells back in his homeland of the Netherlands.
“The 21-year-old left-back, who has also signed a one-year contract extension with Chelsea, will spend 2021/22 in the Championship at Birmingham City.
“Last season he played at AZ Alkmaar where he mostly featured in their second string and then at Den Haag where he made 17 first-team appearances.”
