Neymar has been taken to hospital for tests after he was stretchered off during Brazil's 2-1 win over Colombia.
The 22-year-old was kneed in the back by Juan Camilo Zuniga with two minutes of the match left to play and appeared to be in some distress.
The extent of Neymar's problem is unknown, but his loss would be a huge blow for Brazil, who will be without the suspended Thiago Silva for their World Cup semi-final against Germany next week.
Goals from Silva and David Luiz helped to book Brazil's spot in the last four, despite a late consolation from James Rodriguez.
