Wales and Lions captain Sam Warburton has been ruled out of action for up to four months.
Warburton suffered an injury to his hamstring playing for the British and Irish Lions in the second Test against Australia in Melbourne.
It forced him to miss the third and final match in Sydney where Alun Wyn Jones took over the captaincy.
If the Cardiff Blues back row needs the full four months to recover he is likely to miss the November internationals where Wales will face South Africa, Argentina, Tonga and Australia.
The Blues head of medical John Miles told the club's website: "Sam suffered a grade three tear to his left hamstring in the second Lions test against Australia on the 29th of June.
"He has had a scan with specialists in London on Thursday which has shown the injury is already healing.
"He therefore does not need surgery but will require a period of rehabilitation between 12 to 16 weeks from the date of the injury.
"His rehabilitation will focus on range of motion, flexibility and specific strengthening of the hamstring in order for him to return to full health."