The 23-year-old only joined the Black Cats in January, from Turkish Super Lig outfit Bursaspor, and he made 16 appearances in the second half of the season.
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The Wearsiders confirmed the deal with a brief statement on their official website.
N'Diaye, a France youth international who has represented his country at Under-21s level on one occasion, will now link up with an Eskisehirspor side who finished eighth in the Super Lig last season.