The two-times capped Welsh international picked up a knee injury during the Men of Gwent's' 32-28 victory over the Ospreys last Friday.
It is now feared the 24-year-old could be set for a substantial period on the sidelines to end his Magners League season and leave his World Cup dreams in tatters.
"We're still waiting for confirmation but it doesn't look particularly good," said Dragons forwards coach Danny Wilson.
"He's gone off for scans this week but realistically I can't see him playing again this season."
Harries made his Wales debut during the tour of New Zealand last June and also featured against Australia during the autumn internationals before missing out during the Six Nations.
He had been targetting a return to the Welsh set-up in time for the trip to the land of the long white cloud in five months time but that now looks unlikely.
"His chances seem pretty slim but you never know with ligament injuries and it may not be as bad as we first thought," added Wilson. "We've sent him through the right routes to make a proper decision."
The injury also leaves the Dragons facing another injury crisis. Martyn Thomas, Matt Evans and Pat Leach are all currently sidelined through injury, with Leach the only contender near a return.
"It's quite apparent that we don't have an out and out 15. Pat is making really good progress from his injury and we hope to have him back in contention next week for the game with Cardiff Blues.
"But we have guys in this squad who would suit different types of games. We're looking at two options for the game with Edinburgh but we will make a decision later in the week."
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