Stuttgart have warned potential suitors of Vedad Ibisevic that they have no intention of selling the striker.
Juventus midfielder Arturo Vidal has told the Italian press that he will not be going to Manchester United this summer.
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.