Williams, Wales' record try-scorer with 54 Test touchdowns in 82 Tests, has said several times that this season will be his last at the highest level.
But whether that is after the current World Cup campaign or the RBS 6 Nations Championship later this term remains to be seen.
At 34, Williams remains arguably the most potent attacking weapon available to Wales coach Warren Gatland, and his match-winning ability could be key in Sunday's critical Pool D clash against Samoa.
"I've said that this is going to be my last season with Wales," said Ospreys speedster Williams.
"I am not really thinking about it (retirement) at the moment. My concern is to train well and get selected for these World Cup games.
"This is only my third game since March. As far as I am concerned, I never want to retire. I love playing for Wales.
"But you have got to be realistic as well. You have got the likes of George North, Leigh Halfpenny and Aled Brew coming through, and you are not going to get selected forever.
"We will wait and see. It is not written in stone that this will be it, but I am being realistic as well.
"It is getting to the twilight of my career. I still love it as much as I did when I played my first game for Wales, it's just these younger guys there are almost ready to take the mantle and move on.
"I just want to think about the next game for Wales, and that is Samoa, and being successful in this World Cup."
If Wales can repeat the intensity and accuracy of their performance against world champions South Africa last Sunday, then it should prove enough to subdue a Samoan side fancied by many as serious Pool D contenders.
And Williams believes the Wales squad has dusted itself down sufficiently following the agony of a one-point defeat in Wellington and are ready to go again.
"We are fed up of coming close against the big sides and not winning," he added.
"From that side of it, it was difficult to take because you can't get any closer than that to beating a class side like South Africa.
"But we have picked ourselves up really well. The more experienced guys have helped the younger guys through.
"The thing you can't dwell on is the fact we lost. We have three remaining group games. We have to win them all, and there is a very short turnaround, so you just have to think about the next game.
"It is in the back of your mind that you could have beaten the world champions, but we have got a task ahead of us on Sunday. "We've trained very well, and there doesn't seem to be any hangover."
Gatland will announce his team tomorrow, with few - if any - changes expected following the Springboks game, a match that saw Wales report no fresh injury concerns.
Prop Gethin Jenkins and fly-half Stephen Jones are both training again after being sidelined by calf muscle injuries, with places on the bench seemingly possible for both.
Assessing Samoa's challenge, Williams said: "South Africa are one of the most physical teams out there, and certainly Samoa are as well.
"What you find with South Africa is they are very structured in their physicality, but with Samoa you've got the likes of (Seilala) Mapusua and (Alesana) Tuilagi, who will come out of the line and put massive hits in.
"In that sense it is a little bit different, but Samoa are very structured as well these days.
"They seem to compete at the breakdown a lot more than they ever have, so it is going to be as physical as any game you are going to play.
"Hopefully, we can compete with that, but not only compete, also negate their physicality and create things against them."
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