Mitchell was placed on injured reserve prior to the Bills' season opener against Miami after he hurt his foot in practice.
The seven-year pro was coming back from a right knee injury that forced him to miss the final 11 games last season after he went on injured reserve.
Coach Chan Gailey declared McGee as questionable.
The unit will get a little boost, though, when starting inside linebacker Paul Posluszny returns after missing two games because of a right knee he sprained in Buffalo's season-opening loss to Miami.
Information from The Associated Press was used in this report.