Indeed, berserkers had much in common with those thought to be werewolves. Ulf, a retired berserker, is mentioned in this light in Egils saga Skallagrimsonar:
But every day, as it drew towards evening, he would grow so ill-tempered that no-one could speak to him, and it wasn't long before he would go to bed. There was talk about his being a shape-changer, and people called him Kveld-Ulf ["Evening Wolf"]
(Palsson and Edwards, Egil's Saga, p.21).

In Volsunga Saga, Sigmund and his son Sinfjolti steal the wolf-skins which belong to two "spell-cound skin-changers" to change into wolves themselves so that they might go berserking in the woods (R. G. Finch, trans. The Saga of the Volsungs. London: Thomas Nelson Ltd. 1965. pp.
10-11).

In the sagas, berserks are often described as being fantastically ugly, often being mistaken for trolls, as were Skallagrim and his kinsmen in Egils saga Skallagrimsonar (Palsson and Edwards, Egil's Saga, p. 66). Egil himself is described as being "black-haired and as ugly as his father" (Ibid., p. 79), and at a feast in the court of the English king Athelstan, Egil is said to have made such terrible faces that Athelstan was forced to give him a gold ring to make him stop:

His eyes were black and his eyebrows joined in the middle.
He refused to touch a drink even though people were serving
him, and did nothing but pull his eyebrows up and down, now
this one, now the other.. (Ibid., pp. 128-129).

In Arrow-Odd's Saga, the berserk Ogmund Eythjof's-killer is similarly described as having a horrible appearance:

He had black hair, a thick tuft of it hanging down over his face
where the forelock should have been, and nothing could be
seen of his face except the teeth and eyes.... for size and
ugliness they were more like monsters than like men                                                      (Paul Edwards and Hermann Palsson, trans. Arrow-Odd: A Medieval Novel. NY: New York U. P. 1970. p 37).