Obi joined Middlesbrough from Chinese club Tianjin TEDA on a short-term deal in January transfer window but scored one goal in 19 games.
However, Mikel Obi will join Stewart Downing, Dimi Konstantopoulos and Andy Lonergan to leave the Riverside this summer.
Middlesbrough made the announcement through their official twitter handle and it read:
“Stewart Downing, @Dimster23, @mikel_john_obi and @lonners24 are set to leave #Boro this summer,”
— Middlesbrough FC (@Boro) May 30, 2019