Harries was taken from the field at Rodney Parade in the first half with the injury and he now faces a race against time to try and force his way into Warren Gatland’s World Cup squad.
“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 targeting a return to the Welsh set-up this summer 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.”
