The back-rower was forced off the field during his club side’s 19-10 triumph over Montpellier in the Champions Cup and national team head coach Gregor Townsend confirmed the worst.
“To lose someone like Hamish is disappointing,” Townsend said. “But it is an opportunity for someone else.”
Scotland also have concerns over three other players, with Sam Johnson, Jonny Gray and Ryan Wilson currently nursing injuries.
They open the tournament with a game against Italy, a match the Scots are expected to win comfortably, but Townsend is not taking them lightly.
He added: “The expectations in Scotland will be high, but we realise that it is a very tough game to start with.
“We have lost a number of times to Italy and we should have lost to them last year. They are a very tough team to play against, and Scotland teams in the past have found it very difficult.
“We are in it to win it [the Six Nations], and I imagine that is what every team is focused on.
“Finding that consistency of good to very good performances is what is required from us to be tough to beat, and to win tournaments.”
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