Jozy Altidore was knocked out during AZ Alkmaar's 1-1 draw with NEC Nijmegen on Wednesday night.
The Dutch clubs leading scorer was involved in a collision with NEC defender Pavel Cmovs just prior to the half-hour mark and could only return to the pitch for two more minutes before he had to be replaced.
22-year old Altidore suffered head, neck and back injuries but it is still unknown just how bad the problem is for the former New York Red Bulls and Villarreal man.
USA national team coach Jurgen Klinsmann will be hoping he is ok as he looks to put a squad together for upcoming friendlies with Scotland and Brazil.
