Simons made his debut in the Carabao Cup last season before agreeing a new contract at Stamford Bridge, which includes an option to extend his stay to 2024.
The defender becomes the 16th player to leave Chelsea on loan this summer.
Romelu Lukaku, Callum Hudson-Odoi and Levi Colwill are among those to have also left on a temporary basis with Baba Rahmann re-signing for Reading on Wednesday.
