French media have revealed the reason Dan Carter failed a medical examination, forcing Racing 92 to pull out of a lucrative three-month contract with the former All Black first-five.
Carter, who left Racing in July last year to join Japanese side Kobe Kobelco Steelers, was signed as a short-term replacement for South African Pat Lambie, who was recently forced to retire after several concussions.
He was expected to join the Parisian outfit on March 10.
Racing announced on Sunday, however, that they had withdrawn their offer on medical advice.
"As part of routine medical checks prior to the approval of players' licenses, Racing 92 forwarded certain medical information to experts appointed by the Ligue Nationale de Rugby (LNR). Their opinion was unanimous: Dan Carter will not be able to play rugby in France," the club said in a statement.
According to Le Parisien, Carter "suffers from a cervical spine problem" that prohibits him from re-joining as per the regulations in French rugby.
Sport24 reported Carter's neck issue is similar to that of Saracens' French prop Christopher Tolofua, who last year had his contract with Toulon canceled last minute when his cervical spine was classified G3 following medical examinations.
The legislation is different in other countries, allowing Carter and Tolofua to continue playing in Japan and England, respectively.
Racing 92 was heavily criticised after announcing the 36-year-old's signing last week, with reports he would earn between €20,000 and €30,000 (NZ$33,00–NZ$49,000) per month.
"Everybody talks about the big return of the star, whereas it's a guy of 36 years old who will take the place of a young Frenchman," Carcassonne coach Christian Labit said.
"I take offense to those who boast of singing these men and who advertise that it is the messiah who arrives. I would have preferred if we are Racing, that we take the small number 10 and prepare it, but we prefer to be reassured by going looking for Carter. It annoys me."
Carter, meanwhile, has remained silent on the issue - posting a series of training videos to Instagram while on holiday with his family in New Zealand.
The 112-cap All Black and his family have been spending time in Taupo, Southbridge, and Windwhistle after completing his debut season at the Steelers.
Carter was named MVP of the Japanese Top League after leading his side to the title in his debut season.
He was also named the top kicker with a 86.2 per cent success rate across the competition.