Rory Best's participation in Ireland's November internationals has been thrown into doubt with the hooker set to be out for up to six weeks with a hamstring problem.
The Ulster and Ireland captain sustained the injury in training last week, with his club confirming on Monday he had suffered a tear.
"Following a scan, it has been confirmed that Rory Best has a hamstring tear and will be out of action for approximately 4-6 weeks," a brief statement read.
Best has not played any rugby since the British and Irish Lions' tour of New Zealand in June, and he looks certain to miss Ulster's next three Pro14 fixtures, as well as their opening two Champions Cup matches against Wasps and La Rochelle.
Following a scan, it has been confirmed that Rory Best has a hamstring tear and will be out of action for approximately 4-6 weeks pic.twitter.com/3lTCeiRUT9-- Ulster Rugby (@UlsterRugby) September 18, 2017
Ireland are scheduled to play three internationals later this year, against South Africa, Fiji and Argentina, with the Springboks the first to visit Dublin on November 11.
Best is unlikely to have played much if any rugby by that stage, meaning head coach Joe Schmidt may not wish to take a gamble on his skipper so soon after injury.