The Brazil superstar suffered the injury in the warm-up match with Qatar and was reduced to tears as he made his way off the pitch.
Neymar appeared to twist his ankle in the 17th minute and was carried to the dressing room with his ankle wrapped in ice.
Brazil boss Tite suggested the injury was not a serious one but Neymar was pictured leaving the stadium wearing a protective boot.
But Brazil’s worst fears have been confirmed ahead of the tournament with Neymar tearing ligaments in his ankle.
Brazil won the warm-up match against Qatar 2-0 thanks to goals from Richarlison and Gabriel Jesus.
Neymar has had a nightmare season with injuries, having been out of action for three months with a foot problem before returning at the end of the campaign.
He was also ruled out of the latter stages of the World Cup in 2014 and injuries have now hampered his involvement in another competition.
The injury comes amid more speculation about his club future with Barcelona working on his return to the Nou Camp.
Like BONA NAIJA on Facebook
Follow BONA NAIJA on Twitter