Fergus McFadden is out for up to six weeks.
A scan after the Munster defeat revealed an ankle strain for the Leinster winger.
Mike Ross is also a concern with a groin strain but isn't yet ruled out of contention for the weekend clash with Zebre.
McFadden will miss the European Champions Cup pool stage games against Wasps and Castres.
With Dave Kearney, Zane Kirchner and Luke Fitzgerald already missing - it leaves the Blues short of attacking options.
Speaking at the launch of the new European competition skipper Jamie Heaslip was asked by 98FM Sport if the injury profile can have a psychological impact on the squad...
