Scotland captain Mike Blair admits the likely loss of Ross Rennie for the rest of the season is a big blow for both club and country.
The Edinburgh flanker has undergone exploratory knee surgery after being injured against Glasgow and the results suggest he will not be fit before the summer.
The 22-year-old forward had only returned to action in October after seven months on the recuperation trail after a knee operation and was banned for two matches for a high tackle on Paul Sackey.
A fit Rennie would have provided a challenge to Glasgow's John Barclay for the open side flanker spot in this year's RBS 6 Nations.
Scotland coach Frank Hadden has already lost the services of wingers Rory Lamont and Nikki Walker for the RBS 6 Nations.
Blair said: "This is a big blow. He was a key guy for Edinburgh last season. I'm sure he can come back as good, if not even better, than he was last season though."