Ryan Jones has withdrawn from the Wales side to take on Australia in the Invesco Perpetual Series climax at the Millennium Stadium on Saturday (Kick-off 5.30pm).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)
A pioneering strength and conditioning programme has been delivered to more than 8000 boys and girls at hub schools throughout Wales this season, helping to develop stronger, more flexible athletes for rugby and other sports.
The Singha Premiership Rugby 7s Series returns to the BT Sport Cardiff Arms Park on July 22nd when all four Welsh regions go head to head. Scarlets skills coach Dai Flanagan and Blues Elite Performance Pathway Manager Richard Hodges along with current Welsh squad members were at the launch of this season's event
GB7s women left their England base to train in Wales this week. Olympic Games hopeful Rachael Burford gives WRU TV's Graeme Gillespie her thoughts on Welsh teammate Jasmine Joyce - a 'one touch wonder'
The GB7s women's squad is currently training at Wales' Centre of Excellence where assistant coach Richie Pugh tells WRU TV's Graeme Gillespie some 'tough calls' will have to be made when it comes to finalising the 12 spots for Rio's Olympic Games.