Ryan Jones has withdrawn from the Wales side to take on Australia in the Invesco Perpetual Series climax at the Millennium Stadium on Saturday (Kick-off 5.30pm).
Gethin Jenkins will captain the team and Jones is replaced at No8 by Andy Powell, who moves across the back row, with Dragons flanker Dan Lydiate promoted from the bench to the blindside to win his second cap.
Lydiate's place as a replacement is taken up by Sam Warburton, who faces the prospect of tackling the Wallabies for the second time in a week after representing the Cardiff Blues against their midweek touring side on Tuesday.
"Ryan pulled up in Tuesday's conditioning session with a back problem," said Wales physio Mark Davies.
"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."
Sam WARBURTON (CARDIFF BLUES - Cap No 1,070)
DoB: 05.10.88. 1.88m / 6'2". 15st 9lbs / 99kgs
International record: 2 caps (W 2)
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Go to www.wru.co.uk/tryourgame for more information
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WRU Head of Rugby Josh Lewsey met with volunteers across the game earlier this week, championing their role in the sport. He was joined by Wales captain Sam Warburton for part of the day as volunteers took part in a 'Try Out' event for the 2015 Rugby World Cup