The 26-year-old is reported by French media to have suffered serious spinal injuries before being taken to University Hospital of Rouen.
 
Nice chief executive Julien Fournier told L'Equipe: "In the light of the information currently available to us, the situation seems quite serious. We are worried.
 
"I am in touch with Kevin's family and we are awaiting the medical verdict.
 
"We will follow it hour by hour and obviously stay with him."
 
Anin made only 13 appearances for Nice last season after suffering with mental issues, his only goal was a stunning winner in the Cote d'Azur side's 4-3 win over Toulouse in April.