Acuna hospitalised by Ajax fans
The two sides are bitter rivals, and only the previous weekend Rotterdam police made 53 arrests during the Dutch first division clash between the two sides.
However, according to Feyenoord's official website, on this occasion a large number Ajax fans invaded the Toekomst pitch and attacked Chilean Acuna and winger Robin van Persie (pictured).
"It was complete chaos," said Feyenoord's coach Mario Been.
"My players laid everywhere and they had to be saved by John van't Schip and Daniel de Ridder."
Acuna suffered head, neck and rib injuries in the incident, but his injuries are not believed to be serious.