The contracts for both players expire during the summer and will not be renewed.
Christie scored 9 goals in 29 starts (+20 as sub) in his injury hit four years at the Riverside. Graham started just twice (+19 as sub) and scored two goals. He also enjoyed loan spells at Derby, Leeds and Carlisle.
Another player possibly on the move is winger Nathan Porritt. The highly rated 17-year-old has been given permission to talk to other clubs and has attracted interest from top clubs in England and across Europe.