Cardiff Blues openside Martyn Williams suffered a broken arm in the loss to Ulster on Friday night.
Williams, who started all three of the opening RaboDirect PRO12 fixtures for the Blues this season, suffered the break in the 67th minutes of the match and was replaced by Thomas Young. The Blues also have Josh Navidi and Academy flanker Ellis Jenkins to call on ahead of Friday night's match against Munster.
It is another blow for the veteran flanker who was left out of Warren Gatland's 30 man squad for the Rugby World Cup having reached 99 caps for Wales. He is expected to be out of action for a minimum of six weeks.