Cardiff flanker Thomas Young will be out of action for up to three months after suffering a torn calf tendon.
Young, 30, limped out of the United Rugby Championship defeat against Scarlets on 7 January.
The injury rules him out of any potential Wales recall for next month’s Six Nations.
Young was not included in Wayne Pivac’s autumn internationals squad with Warren Gatland taking over from his fellow New Zealander as Wales head coach.
Young has scored four tries in 12 games for Cardiff this season and been one of the form flankers in Welsh rugby after re-joining from Wasps in the 2022 summer.
He came through the ranks of Cardiff making 19 first team appearances during his first spell with the club before spending nine years with Wasps and made more then 200 appearances for the English club.
Wales full-back Liam Williams and centre Rey Lee-Lo also came off the field against Scarlets and are undergoing head injury assessments (HIA) ahead of the home Challenge Cup match against Newcastle on Sunday, 15 January.