Hardwick said the Tigers were yet to determine the best way to replace the five-time All Australian.
However, possible inclusion Ryan Garthwaite will not face the Magpies and is likely to need one more week at VFL level before being declared fit after Achilles soreness, meaning the Tigers could use versatile tall Noah Balta, who made his debut last week, in defence.
Running half-back Oleg Markov could also come into the side and he trained with the main group on Wednesday at Punt Road, as did small forward Liam Baker.
Brandon Ellis, who picked up 40 disposals last week, appears a strong chance to replace Houli for the Thursday night MCG blockbuster.
Source: AFL website