Cory Hill has been released from Wales' Rugby World Cup squad due to injury.
Dragons lock Hill was named in the squad and travelled to Japan, but he has not been able to recover from a stress fracture of his fibula.
Hill, who has not played since February, will be replaced by 65 times-capped Ospreys forward Bradley Davies, the Welsh Rugby Union announced.
The WRU said: "Cory Hill has been released from Wales' 2019 Rugby World Cup squad after being unable to recover significantly from a stress fracture of his fibula.
"He will return to Wales and continue his recovery with his region.
"Bradley Davies, capped 65 times by Wales and who has featured in two previous Rugby World Cups, has been named as his injury replacement and will arrive in Japan on Wednesday."
Wales, who opened their World Cup campaign with a 43-14 win over Georgia on Monday, had hoped that Hill would be available to face Australia in a Pool D showdown next Sunday, but he has run out of time.
Hill's fellow lock Adam Beard, meanwhile, only arrived in Japan three days ago after having his appendix removed.
Skipper Alun Wyn Jones and Jake Ball are set to continue as Wales' second-row partnership against Australia, with flanker Aaron Shingler providing lock cover on the bench.
Victory for Wales against the Wallabies would put them in pole position to top their group and book a possible quarter-final against France or Argentina.
Speaking to reporters in Tokyo, Wales' World Cup attack coach Stephen Jones said: "It is unfortunate for Cory. He's such a wonderful person. It's just unfortunate.
"Bradley is a great man with vast experience and two World Cups behind him, so he brings that experience into the squad."