The 58-times capped All-Black was taken off after 37 minutes of Munster's 30-20 Celtic League loss to Cardiff on Saturday, and yesterday's examination backed up coach Alan Gaffney's worse fears.
With Cullen facing 4-6 months on the sidelines, and the ERC deadline for registering additional players for the Heineken Cup's knock-out stages this Thursday, Gaffney admitted: "Obviously we have been exploring that situation over the past while. Now we have to re-visit the issue with a different midset in light of the injury to Christian. We have until Thursday to nominate and we will be making no decision until then."
"It's particularly tough on him however and I can only wish him well in his recovery."