Wales coach Mike Ruddock was the first to pay tribute to Llewellyn's impressive contribution to Welsh rugby and he says the 36 year-old lock is still in contention for selection in the remaining matches of the campaign.
"We are disappointed to lose a player who has provided such quality and commitment to the national cause," said Ruddock. "Gareth is a determined and vastly experienced individual who is still in great condition. Only recently he recorded a personal best in speed trials with the national squad and he is still very much a valued member of our squad.
"We have discussed the matter of his retirement and with the current situation we have found it difficult to guarantee that Gareth will be a part of our plans next year and so he has taken this decision, but it is certainly possible that he will play himself into the side before the end of the tournament.
"He has the strength of character to want to battle for a spot in the starting line up at this stage in his career and he has always been that way. Whilst it was inevitable that at some stage he would decide to hang up his international boots, I know that he will be battling just as hard as he ever did to get back on the pitch before that final whistle blows on his Wales career.
"He has been, and still is, a great player and that is why we persuaded him that he was an important part of our plans this season. He has been instrumental in helping the youngsters in the squad come good in recent years and we know he won't be going without a fight.
"If he appears again for his country, it won't be through any misplaced sentiment, it will be because he has played himself into the team, as he has done so often."