The 35-year-old is in the twilight of his playing days, and was offered a one-year deal with the Welsh club in what would likely have been his final year as a professional player, but the move has been denied by the WRU due to concerns that his presence within the squad could halt the progress of a homegrown player.
Williams, who played four times for the Junior All Blacks as well as the Auckland-based Blues and North Harbour during the first four years of his 15-year career between 2004 and 2008, is still at the peak of his powers, as shown in a man-of-the-match performance during his side’s season-ending 26-23 defeat to Ospreys at Principality Stadium on Saturday.
Following the match, Cardiff head coach John Mulvihill expressed his desire to keep Williams on board at the club.
“I hope so, but that’s beyond me,” he said.
“I am keen to have him stay and play and he’s keen to do that as well.
“We will just have to wait and see what the next few weeks bring.”
Mulvihill went on to praise his star No. 8’s showing against Ospreys on the final day of the 2018-19 Pro14 regular season, which doubled as the Judgement Day double-header for all four Welsh provinces in the competition.
“I thought he played a good 80 minutes,” Mulvihill said.
“You dare not take him off with five to go because you will get the evil eyes.
“He was good. He was our heart and soul.”
Williams left New Zealand at the end of 2008 to join Irish side and Cardiff’s Pro14 rivals Munster, and after stints with now-disbanded Italian club Aironi and the Belfast-based Ulster, he signed with Cardiff ahead of the 2016-17 campaign.
Currently residing in the Welsh capital with wife and three daughters, Williams and his family have long-term plans to stay in Cardiff.
“I won’t be returning to New Zealand,” he told Wales Online.
“My wife and I will be settling in Cardiff with our three girls. We have decided to set our roots here in Barrybados.
“I have been in Europe for 12 years now and have had all three of my babies up here, so it seems the right thing to settle here with my mates and connections, who have also become family.
“It has become a home from home away from New Zealand. It was only when I went back for my brother Tim’s [Nanai-Williams, Clermont’s and Samoa’s utility back] wedding that I landed in Auckland and it didn’t feel like home.
“It will always be a special place and I will always be thankful to Auckland and New Zealand for what they have given me in regards to rugby, but you have to move on.”
Should there be no viable way for Cardiff to retain him through a contract extension, Williams has suggested he may pursue a job in security once he retires from professional rugby.
Sign up to our mailing list here and we’ll keep you up to the minute with weekly updates from the world of rugby.