The 25-year-old sustained the injury in Edinburgh’s 27-13 loss to Ospreys in Swansea last Friday, which was his first appearance for the club since October 2014.
Gilchrist has endured a tortuous 16 months since he broke an arm in the European Challenge Cup clash against Lyon just after Scotland head coach Vern Cotter had selected him as his captain for the 2014 autumn Test series. He missed the rest of the season but battled back to make Scotland’s World Cup squad after missing another chance to skipper his country when he was struck by illness on the day of the warm-up Test away to Italy in Turin.
More disappointment was around the corner when a groin injury ended his tournament during the pool clash against the United States in Leeds.
That injury suffered complications and it was only last week that Edinburgh coach Alan Solomons named him on the bench for the Guinness Pro12 clash in Wales.
After so long out it would have been a push for Gilchrist to play a part in this year’s Six Nations but there was a chance he could have been involved in the last two rounds.
An statement released from BT Murrayfield last night read: “Edinburgh Rugby is disappointed to report that lock Grant Glichrist sustained a fracture to a long bone in his forearm during a collision in Friday night’s Guinness Pro12 match against Ospreys at the Liberty Stadium.
Gilchrist has seen a specialist and will undergo surgery.
An Edinburgh spokesman said: “The injury sustained is not to the same bone that required medical attention prior to Rugby World Cup 2015.”