Dan Carter's shock decision to join the Auckland Blues has riled up fans of his former side Canterbury Crusaders to such an extent that even his father hopes the former All Blacks fly-half will be on the losing team when they meet in July.

The 38-year-old Carter, who played for the Crusaders from 2003-15 before moving to France, surprised many on Thursday when he signed with the Blues for New Zealand's Super Rugby Aotearoa competition, which starts on 13 June.

The Canterbury-Auckland rivalry is the fiercest in domestic rugby and Carter's father Neville said he would back his hometown Crusaders over his son and his new Blues team-mates.

"It's pretty straightforward," he told Newstalk ZB. "The Crusaders are always going to get the support from me.

"And I'll just keep my fingers crossed he's not going to get smashed by them."

The Blues play the Crusaders on 11 July in Christchurch and the three-times World Rugby Player of the Year, who is still weeks away from being match-fit, should not expect a warm welcome, said Neville.

"I did say to him, 'You may be getting a bit of a bad reception when you get down our way,'" he added.

Carter spent the last two seasons in Japan with Kobelco Steelers before the novel coronavirus outbreak ended the 2020 Top League campaign.

There was little sign of any goodwill for his time at the Crusaders when TVNZ interviewed rugby fans on the streets of Christchurch, with Carter's picture in a Blues jersey being treated with disdain.

One local even joked he was "a traitor".

Carter had been on the brink of joining the Blues twice earlier in his career, only to remain loyal to the Crusaders with his grandmother Pam talking him out of the move on one occasion.

She told TVNZ she was okay with his move this time.