Matthew Rees has been ruled out of action for ten weeks after undergoing successful neck surgery.
The Wales and Scarlets captain had been suffering from a disc-related neck problem but was hopeful that he would be available for selection for the World Cup.
The 30-year-old had been taking pain-killing injections in a bid to be ready for next month's tournament in New Zealand but he was eventually ruled out.
"The operation went very well," said Scarlets head coach Nigel Davies.
"Matthew is very good and we are hoping he will be available within eight to 10 weeks."
Rees could make his return for Scarlets against against Ospreys in their Wales Pro 12 league derby clash on Saturday, November 5.
Wales begin their World Cup campaign against South Africa on Sunday, September 11.
