Former All Black Jerry Collins may have been threatened and had reason to fear for his safety in the weeks leading up to his arrest, his agent says.

Collins, 32, was arrested at the weekend in the central Japan industrial city of Hamamatsu on charges of illegally carrying a kitchen knife in a department store, police said yesterday.

Former All Black Jerry Collins. Credit:Reuters

He told Japanese police he kept a kitchen knife for ''self-defence''.

Collins Wellington-based manager Tim Castle said details were still sketchy, but he had heard that there may have been an incident involving social media that gave Collins cause for concern.