The full-back, who has only played in four SPL games this season, is out with a hamstring injury - just three weeks after returning from a similar knock.
Boss Jim Jefferies said: "Garry pulled up in the final minute at Tannadice and hurt the opposite hamstring to the one he did before.
"It's a huge blow, especially with Frazer Wright about to serve a two-game ban.
"Allan Johnston and Grant Murray are back to full fitness but just when we get a couple back we lose another one."
Meanwhile, Jefferies hopes defensive duo Simon Ford and Frazer Wright will sign new contracts this week.
He said: "We've offered both players two-year deals with an option of another year.
"We're very close to tying up Simon and I've had word back from Frazer's agent that there's just one thing we need to sort.
"I'll discuss that with the chairman over the next couple of days and hopefully Simon and Frazer will be tied up by the weekend.
"They are important players for us and have both done well over the last couple of seasons. "They enjoy it here and want to stay which is great.
"Simon's only been on a short-term contract but has done more than enough to convince me he deserves a longer deal.
"Frazer's also done really well.We took a bit of a chance on him when we signed him from Stranraer two years ago but he's worked ever so hard and has made fantastic progress in that time.
"They both know we're restricted in what we can offer but we've tried to give them the best deals we can."