Hartlepool have announced they will not sign convicted rapist Ched Evans after boss Ronnie Moore expressed an interest.
Arsenal manager Arsene Wenger insists he will only spend money in January on the right player.
Hackett, 29, made 145 appearances for the Lions, scoring five goals, since joining from Hearts in 2006.
However, he slipped out of the first-team picture this season and ended the campaign on loan at Wycombe.
Former Leicester and Watford full-back Stewart, 30, endured an injury-hit season since he signed last summer and managed just seven appearances.
Youngsters Jake Gallagher and Conor McLaren have also been released.