Bradley Davies has sustained an ankle injury while training with Cardiff Blues.
The Wales lock will need surgery to repair ligament damage, which could keep him out of the Six Nations.
A statement from the Blues said: "Bradley will have an operation early next week and an accurate timescale on his recovery will be assessed after the operation."
Wales are also without Alun Wyn Jones and Luke Charteris from their second row, while Ian Evans could return in time for their Six Nations' opener against Ireland on February 2.
