London - Adam Beard and Cory Hill face a race against time to prove their fitness for Wales' World Cup opener against Georgia.
Ospreys lock Beard is set to join the Wales squad early next week after having his appendix removed.
Beard, who has won 16 caps, was admitted to hospital in Wales ahead of the squad's departure for the tournament in Japan on Wednesday.
Hill is recovering from a stress fracture in his leg, with the second group fixture against Australia on September 29 his initial target to return.
Wales still hope that 23-year-old Beard will be available to face Georgia in Toyota City on September 23.
If Beard and Hill are absent, it could mean Scarlets flanker Aaron Shingler providing second-row bench cover.
Welsh captain Alun-Wyn Jones and Jake Ball are likely to start against Georgia however.
"Adam Beard was admitted to hospital in Wales with suspected appendicitis by Wales team medics ahead of the squad's departure last Wednesday," a Welsh Rugby Union spokesperson said on Thursday.
"He had his appendix removed uneventfully later that day and is recovering well.
"He will rejoin the rest of the squad in Japan early next week."