The story opens with a crew of Vikings having landed in what is now North America. I do not recall if this was by accident, shipwreck, or intent. I do recall that the protagonist is a jaded sort. I seem to recall a line where he expresses disgust for the behavior of most of his other shipmates. One of the Vikings he is still friendly with, his best friend in fact, remarks something along the lines of "you've had many an Irish nun beneath you." The line pointing out that the protagonist has been as savage in the past as those he condemns now, and also expressing concern for his friend's troubled outlook.
As the story progresses, the other Vikings begin to be murdered, one by one. With each killing, the fear and tension of the remaining Vikings increases. I cannot recall if they suspect the protagonist, though it sticks in my mind he grows increasingly alienated from the rest of the crew. It also sticks in my mind their fear is fed by legends of werewolf-like beasts.
Near the end of the story, only the protagonist and his best friend are left. I think it is at this point we learn that the transformation was born out of a collective fear or belief. The protagonist asks his friend if he believes he is still the same man as before. That the friend believes that to be so, is the reason the protagonist has never changed into a werewolf around him and/or attacked him. Something like that (I'm a bit fuzzy on the exact phrasing, I fear).
Publication Details and Timeframe
I'm almost 100% certain I read this is a sci-fi magazine, not an anthology. I also am fairly certain the story hails from the 1980s. No idea on who the author might be, though.