Bradley Davies has been ruled out of contention for selection this weekend due to a chipped bone in his neck.
Luke Charteris has been called up to the Wales tour of North America to replace Blues lock Bradley Davies, who has been forced to withdraw from this Saturday's Test against USA with a chipped bone in his neck.
Davies came off during Wales' 32- 23 victory over Canada on Saturday and a scan has revealed the injury which will see him in recovery in four to six weeks.
Dragons second row Charteris was named in caretaker head coach Robin McBryde's original training squad for the tour, but stayed in Wales to help his region's Heineken Cup play-off ambitions.
After the Dragons secured their Heineken Cup place for the 2009/2010 season with a 42-17 victory over Calvisano last weekend, Charteris automatically joined McBryde's standby list awaiting the call to international duty.
"We are all disappointed for Bradley who played well against Canada and he is a young man with a big future at this level," said McBryde.
"Hopefully he has learned from the experiences he has had already and he will remain with us in Chicago to help out behind the scenes and continue that learning proccess.
"He is up and about and well in himself and we wish him a speedy recovery as he looks to get back on the pitch in time for the beginning of the season with the Blues.
"Luke has arrived in Chicago, he is a more than able replacement and we are expecting him to slot seamlessly back into the system."
Nearly 40 players were involved in the first Wales Under 18 training session of the season. WRU National Performance Manager Gethin Watts is excited at the potential shown by the group and expects the Regional Under 18 Championship to hone their skills even further.