Cusiter started two matches in this year's RBS 6 Nations against England and Wales and also travelled to Australia and the Pacific Islands, helping his country to an undefeated summer tour.
His absence leaves an intriguing contest for the Scottish number nine jersey this autumn in matches against New Zealand, South Africa and Tonga with Mike Blair and Rory Lawson both now playing in the second flight in France and England respectively.
However Glasgow Warriors head coach Gregor Townsend believes Cusiter will still have a significant part to play in his side's season when he returns from injury before Christmas, leaving him plenty of time to win back a spot in Andy Robinson's Scotland squad for the 2013 RBS 6 Nations.
"Everyone at Glasgow Warriors is disappointed that a quality player like Chris Cusiter is likely to be out of action until around the middle of December," said Townsend.
"It's encouraging, though, that he doesn't need surgery, and we know he's in the best possible hands with our medical team.
"Chris is a tough competitor, and he'll be working hard to return to fitness and make a significant contribution to our campaign."
Scotland head coach Robinson added: "It's disappointing for Chris because he has made such a good start to the season. I wish him a speedy recovery."