Alan Stubbs’ side, who have lost their last two matches, must take on their play-off rivals without the services of the club skipper after he picked up an injury in training during the week.
Stubbs had originally thought the hamstring problem would keep Gray out for the remainder of the season but scans have revealed a three to four-week break is more likely.
And Queen of the South counterpart James Fowler, who signed an extention to his current deal during the week, has also been forced into a reshuffle for the vital match at Easter Road.
Influencial midfielder Mark Millar has been ruled out with a broken hand and he will be assessed during the week with a huge home match against Rangers coming up next Thursday.
Like Hibernian, Queen of the South will be desperate to get their promotion push back on track after losing their last two games to Hearts and Raith Rovers, the latter also inflicting a loss on Hibs just days after they crashed 2-0 at home to Stuart McCall’s Rangers.
Speaking to Standard Sport Fowler said: “It’s a blow for us as Mark is a quality player who has been playing well.
“It happened in a collision on Saturday. He came over to the side and got his fingers strapped up but an X-ray revealed a break. He’ll be in plaster until next week and we’ll assess him from there.
“But it gives someone else a chance. We’ve got Stephen McKenna in there and Ian McShane sat out last week so it possibly gives an opportunity for him to come back in.”