The Wales and British & Irish Lions No8, who was due to make a record equalling 28th appearance as national captain in the match against the Pumas, has been replaced in the starting line-up by Andy Powell (Sale Sharks).
Ospreys back five player Jonathan Thomas comes onto the bench to get his first opportunity of the summer RWC warm-up campaign and triple-World Cup veteran Martyn Williams, who will win his 99th cap, has been handed the captaincy.
“Ryan wanted to play and could have played but we have talked it through with him and we didn’t feel we needed to take any risks him this weekend,” said Wales head coach Warren Gatland.
“We have withdrawn him as a precaution and told him we are happy with what he has done so far in terms of making a claim for RWC selection.
“The 30-man squad will be named at the Millennium Stadium on Monday and, without getting ahead of ourselves, we have told him how important he is to us.”
