Accrington Stanley's second round Johnstone's Paint Trophy fixture against Tranmere Rovers was abandoned after 39 minutes due to a serious head injury to Stanley player Thomas Bender.
He was treated for 25 minutes before being stretchered off and taken to hospital.
Accrington assistant manager Jimmy Bell told BBC Sport: "He's been taken to hospital for observation.
"Three players went for the ball and they collided - no one on either side was at fault but our players and Rovers players are really shook up.
"It is a head injury and we are worried about him. We're waiting to hear from the hospital as he wasn't responding at the time."
Chief executive Rob Heys added: "He was starting to show signs of coming around as he left the ground."
Rovers were leading the tie 2-1 before the abandonment.