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The North Berwick-born rugby star faces more than two months out of action after suffering an ankle injury in pre-season against Harlequins.
Muncaster, who turned 25 this week, is set to undergo surgery on the injury after enduring more than his fair share of setbacks.
He missed the end of last season with an ankle ligament injury.
An ankle injury suffered in January last year also kept the back-row man, who has four Scotland caps, out of that year’s Six Nations.
Everitt said in his long coaching career, he had never known a player to have such misfortune with injuries.
“It’s been very bad luck for him,” said the Edinburgh boss. “I haven’t been in a franchise where a guy has been ravaged like that.
“Once this is done, hopefully that’s the end of it and he can move on and get some consistency on the field.”
Muncaster is expected to face about 10 weeks on the sidelines, which would rule him out of the Nations Championships contests with New Zealand, Australia and Japan.