Cooper started his second Test of the autumn when Wales beat Argentina on Saturday, but Dwayne Peel is now in pole position to start against the Wallabies at the Millennium Stadium next weekend.

Warburton, meanwhile, was unlikely to have featured in the match-day 22 when Wales look for their third successive autumn victory.

Wales backs coach Rob Howley said: “This is an opportunity for both players to play in what will be an historic game for the Cardiff Blues.

“In our squad, we feel we have the strength in depth in the back-row and scrum-half to facilitate this request from the Blues to have access to their players.

“Both Gareth and Sam could well have figured in our own plans on Saturday, and are not entirely ruled out should we need to make any changes towards the end of the training week, but obviously they will not be named for Wales when we make our team announcement tomorrow.

“We will incur some disruption to our own preparations, but this decision is about putting the players first as well as backing Welsh regional rugby.

“This way round, we will have two Welsh scrum-halves, and a young man like Sam, all with the chance to start against Australia in a week - a significant development opportunity which would otherwise not have been the case.”

Wales head coach Warren Gatland will now make a switch at scrum-half, and his only other area for debate appears to be in the centre and whether or not he recalls a fit-again Tom Shanklin instead of Jonathan Davies, who started in the 33-16 victory over Argentina.