The injury will definitely rule him out of round two of the Heineken Cup and could threaten his chances of playing for Ireland in the November internationals.
Lions star Easterby is also likely to miss the majority of Ireland's autumn international campaign.
"It was a nasty break and when he came off it was clear that Simon was in a really bad way. It is a great shame because he is a player who has hit real form," said Gareth Jenkins, Llanelli Scarlets director of rugby..
"He will be missed by us and by Ireland in their autumn internationals."
Veteran prop John Davies also needed stitches after the game and fellow international prop Iestyn Thomas and back row man Jon Mills also suffered injuries.