The Official Online RBS 6 Nations Store is open. The store has everything you need to get behind your team during the RBS 6 Nations, plus the store is now fully stocked with a much wider range of rugby merchandise.
His team, Glasgow Warriors, were preparing to face Connacht in the PRO12 at the time.
It was initially hoped he would be out for a fortnight but the damage is worse than what was originally thought.
It means Andy Robinson will almost certainly be unable to select him in the Murrayfield encounters against the All Blacks on November 11, South Africa on November 17 while he will also be a major doubt for Scotland’s clash with Tonga on November 24.
The 21-year-old has won two Scotland caps, both from the bench. He came on as a replacement against France and Fiji earlier this year.
Gregor Townsend, head coach of Glasgow Warriors, said: "It's frustrating for Duncan and ourselves that he's missing out on big games.
"However, with many more important fixtures coming up over the course of the season, it's very important that he gets himself right, and I know he'll be working hard with our medical team to return to the fray in due course."