Dan Carter

But the former All Blacks star was facing one of his toughest challenges this month - growing a moustache to raise awareness about mental health.

"I can't grow a strong mo' (moustache)," Carter, who normally only has to shave about twice a week, said on Thursday.

"I have done bits and pieces over the years but never committed to growing one for a month.

"It's been just over a week and it's pathetic really."

Carter, 38, bowed out of international rugby after leading the All Blacks to victory at the 2015 Rugby World Cup, the three-time World Rugby Player of the Year then spent three seasons in Paris with Racing 92 before joining the Kobelco Steelers in Japan in 2018.

However, the global Covid-19 pandemic put an early end to domestic rugby in Japan in 2020 and Carter decided to return to New Zealand to take up a role with the Blues in Super Rugby Aotearoa.

The 112-test former All Blacks first five, 38, signed for the Blues as injury cover and had been pencilled in on their bench for a 18 July match with the Wellington Hurricanes. Carter, however, suffered a calf strain and was forced to withdraw from the matchday squad.

In a social media Q&A session, he said his expectations of getting game time had been low in any case before the injury.

"I wasn't really expecting to (play) to be honest, unless there was an injury to Beauden (Barrett) or Otere (Black)," Carter said.

"He's pulled up a bit tight," Blues coach Leon MacDonald said.

"It's nothing too major but we want to make sure we don't risk anything with Dan.

"With calves, if you get on top of them early, it can take a couple of days to come right, but if you're a little bit late it can be three to four weeks, so it makes sense just to look after him."

Carter's withdrawal means the full glare of the spotlight will be back on Beauden Barrett, who is returning to Wellington for the first time since his move from the Hurricanes to the Blues.

The new Blues recruit will make the most of the Blues' bye weekend to travel to Canterbury and turn out for his beloved Southbridge club on Saturday.

Carter will pull on the No. 10 jersey at Southbridge Domain against West Melton.

A club spokesperson confirmed Carter's availability for the game on Tuesday evening.

Carter last played for Southbridge in 2014.

His rugby return marks the first major step in his aim to be ready to take on his old team the Crusaders in Christchurch on July 11, in what would be his Blues debut.

Sources have confirmed to RNZ that the former Crusaders star will join the Blues for the Super Rugby Aotearoa competition, which kicks off on Saturday week.

The 38-year-old's signing is expected to be announced at a media session in Auckland at midday.

The Blues coach Leon MacDonald messaged the team on Wednesday to tell them Carter was joining the side as injury cover for Stephen Perofeta.

"His motive is to give back to NZ Rugby by sharing his experience/knowledge with us.

"Great opportunity to learn from one of the games' greats," Macdonald wrote.

In a video interview on Carter’s Facebook page, the former All Blacks captain discussed a time during a match where he inadvertently took away a chance for Carter to eclipse former England first-five Jonny Wilkinson’s all-time record for the most test points scored.

“I only found out that out quite a bit later,” McCaw told journalist Lee McKenzie when asked about the incident. “I was surprised DC didn’t actually tell me he was getting close.

The legendary out-half, who played 112 times for the All Blacks, turned 38 in March and fans will now wonder if the curtain has fallen on a stellar career where he featured for the Crusaders, Perpignan and Racing 92 before joining the Top League. 

Carter - who will turn 38 in March - had surgery last March to mend a cervical spine problem and spent seven weeks in a brace.

But he was back to kick off an 18th professional rugby season in the opening round of the Top League on Sunday.

Carter had not played since December 2018 when he guided Kobelco to the title and picked up Japan's player of the year award.

But the Southbridge scion was soon back into his groove, scoring a try and kicking five conversions and a penalty goal a 50-16 win over the Canon Eagles before 23,004 fans.

Carter beat former New Zealand captain Richie McCaw in the final.

There were 16-players up for the gong and fans voted over a week on head to head clashes to determine the ultimate winner.

All Black halfback Aaron Smith, first-five Beauden Barrett and outgoing captain Kieran Read were also in the mix.

The 37-year-old Carter won World Cups in 2011 and 2015, playing a staring role in the latter after many had written him off as past his prime.

He played 112 tests, winning 99 of them, after debuting in 2003.