Five men and one woman were arrested after trouble broke out at the Johan Cruijff stadium where Ajax was playing Heracles Almelo in their first match of the new season.

Police are now investigating if there is any connection between the trouble on the terraces and another incident in which a steward had a heart attack.

In particular they want to know if the steward had the heart attack after being attacked by a supporter. One rumour doing the rounds on internet says the man grabbed the steward by the throat and then hit him.

The investigation will include questioning witnesses and checking security and other camera footage, news agency ANP said.

That has not yet been confirmed, but Ajax have said the man is making good progress in hospital.

The match ended in a 1-1 draw.