Wales captain Ryan Jones has been ruled out of tomorrow's clash against Australia at the Millennium Stadium.
Number eight Jones pulled up in training earlier this week and he has not regained full fitness in time for Wales’ autumn Test finale.
Newport Gwent Dragons flanker Dan Lydiate is promoted to the starting line-up, winning his second cap, with Andy Powell moving across the back row to wear the number eight shirt.
Cardiff Blues prop Gethin Jenkins will captain the team in Jones’ absence, while Lydiate’s place on the bench goes to flanker Sam Warburton.
Lydiate, 21, made his Wales debut as a replacement during the 33-16 victory over Argentina last weekend, and he has been in outstanding form for the Dragons.
But the loss of Jones is a major blow for Wales boss Warren Gatland, who hopes to mastermind Wales’ second successive win against Australia in Cardiff.
Wales team physio Mark Davies said: “Ryan pulled up in Tuesday's conditioning session with a back problem.
“This obviously needed time to settle and unfortunately the problem has not resolved in time for him to be available on Saturday.
“He has been receiving treatment and was unable to train yesterday, but today we have taken the decision that he is simply not going to be ready to take the field.”
If Warburton features off the bench tomorrow it will be his second appearance in five days against the Wallabies, having played in the Blues’ 31-3 defeat in a tour match on Tuesday night.