Martyn Williams looks likely to be out of action for at least six weeks after breaking his arm during Cardiff's defeat to Ulster.
The veteran Blues flanker, who has started all of his side's RaboDirect PRO12 matches this season, suffered the break in the 67th minute of Friday's match and was replaced by Thomas Young.
The injury comes as another blow to the loose forward after he was left out of Warren Gatland's 30-man Wales squad for the World Cup in New Zealand.
Williams was likely to have been considered as a potential replacement should Wales have injury problems in the back row.
But now the 36-year-old, who is expected to retire from Test rugby after the tournament, looks likely to end his international career stuck on 99 caps for Wales.