Cairns injured his knee initially in a pre-season friendly against Sale Sharks and had returned to full team training as part of his recovery from 'key-hole' surgery.
Unfortunately, in a session in December, he ruptured the joint's anterior cruciate ligament (ACL) with the knee now requiring a full reconstruction.
Cairns will have surgery at the Spire Murrayfield Hospital at the end of January and is expected to return in time for a large part of the club's pre-season, with the opening game of 2012/13 the target for his return.
Edinburgh Rugby lead physiotherapist, Stuart Paterson, said: "There are known risks in rehabilitating a damaged ACL and unfortunately, in this case, the ligament has not been able to withstand the rigours of professional rugby training.
"Rehabilitation guidelines for this type of operation suggest that he'll be available for a large part of pre-season but the important thing is to give his knee time to heal, mature and stabilise.
"Eight months to the date of surgery would be around the time of our last pre-season game and that's an achievable goal for Ben to return to his best."
Cairns said: "As a professional athlete I have the scope to dedicate all my time to making sure I come back healthy."
"I'm taking the positives from this in that at the end of my recovery my knee will be back to 100% and I'll be in the best shape possible, returning faster, stronger and fitter."
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland