The Samoan will undergo further medical examination later in the week to determine the full extent of the injury.
Munster coach Alan Gaffney said:"It goes without saying that I am very disappointed with the news of Brian's injury. He is a vastly experienced and skilful player who would have complemented our squad travelling for what was always going to be a very difficult game.
"In circumstances like this you have to feel for a player who travelled half way across the world to play with us. I know he was looking forward to the challenge. So it's really tough on him. Tough on everyone, but that's the environment we operate in.
"This sort of thing is part and parcel of the job we work at. We have just got to move on quickly and deal with this as we would any setback."