Cardiff Blues head coach Danny Wilson has described Wales star Sam Warburton's latest injury setback as "a major blow for all concerned".
Warburton, British & Irish Lions captain on their last two tours, will miss Wales' autumn Tests this season.
The Blues said that the former Wales skipper faces up to four months out following the recurrence of a neck problem that now requires surgery.
Warburton, who led the Lions in their drawn Test series against world champions New Zealand this summer, had yet to make his first appearance of the season after a post-Lions break before returning to training.
"It's a major blow for all concerned, it's a blow for Cardiff Blues and Wales. We all hoped he would be back playing soon," said Wilson, speaking at the Blues' weekly media session Tuesday.
"It is a long-standing issue that he has had. He gets pain and discomfort on and off. The feeling was that two months off would help it settle completely and do him a world of good.
"He came back feeling confident about it. He went through the protocols when he came back to training and, during the contact element, just on pads, it began to flare up again. We looked into it in more detail and it has led to where we are.
"He is obviously extremely frustrated. He thought that, after two months, he would come back really fresh and that is not the case, but this is the right thing for him to do.
"He is a very good professional and I am sure he will apply himself to his usual standards."